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AMERICAN  SCIENCE  SERIES. 


MODERN    GEOGRAPHY 

FOR   HIGH   SCHOOLS 


BY 

ROLLIN  D.   SALISBURY 
HARLAN  H.  BARROWS 

AND 

.    WALTER  ,S..  TOWER 

Of  the  DepurtmenUof  Gfcgrd^phy.  Vie  Vftivertiiy  of  Chicago 


NEW  YORK 
HENRY   HOLT  AND  COMPANY 


COPTHIGHT,  1913 
BY 

HENRY.-JI0LT-5^'ND.<:cnMPANT  / 


•  •  • 


•  •  «  • 


l>    «  4  •     • 


Printed  in  U.  S.  A. 


PREFACE 

For  several  years  there  has  been  a  widespread  demand  for  a 
course  in  general  geography  in  high  schools.  This  book  is  designed 
to  serve  as  the  basis  for  such  a  course.  All  rational  work  in  general 
geography  must  be  founded  on  physiography,  and  this  fact  has 
determined  the  organization  of  the  material  of  this  book.  Physi- 
ographic processes  and  features  are  treated  briefly,  however,  while 
their  relations  to  life,  and  especially  to  human  affairs,  are  developed 
at  greater  length.  The  book  has  been  prepared  with  the  conviction 
that  the  chief  object  in  geography  teaching  should  be  preparation 
for  everyday  life,  for  citizenship  in  the  widest  sense.  Hence  the 
authors  constantly  have  sought  (i)  to  make  the  text  explanatory 
rather  than  merely  descriptive,  so  that  it  may  afford  training  in  clear 
thinking;  and  (2)  to  emphasize  the  relations  of  earth,  air,  and  water 
to  man's  activities  and  interests,  so  that  the  knowledge  gained  may 
be  directly  useful. 

The  principles  developed  have  been  applied  at  greatest  length 
to  the  United  States,  because  this  country  is  of  most  interest  and 
importance  to  American  students.  Furthermore,  space  forbade  the 
application  of  these  principles  in  detail  to  other  countries. 

The  larger  aspects  of  economic  and  commercial  geography  are 
covered  in  connection  with  such  topics  as  soils,  minerals,  waterways, 
water  power,  harbors,  and  the  distribution  and  development  of 
industries  and  cities.  It  is  hoped,  therefore,  that  the  book  may  be 
found  useful  by  teachers  of  commercial  geography,  as  well  as  by  those 
who  have  sought  to  "humanize"  high  school  physiography. 

The  illustrations  are  intended  to  serve  as  the  basis  for  classroom 
discussions  and  quizzes,  and  should  be  studied  and  interpreted  as 
carefully  as  the  text  itself.  The  questions  may  be  used  for  written 
work  or  for  classroom  discussion.  The  answers  to  most  of  them  are 
not  to  be  found  in  the  text,  but  can  be  reasoned  out  by  students  who 
have  followed  the  text  with  understanding.  The  physical  maps  at 
the  end  of  the  book  afford  the  means  of  locating  most  of  the  places 
and  features  mentioned  in  the  text. 


vi  PREFACE 

Teachers  using  this  book  will  find  it  helpful  to  have  the  authors' 
Elements  of  Geography.  The  larger  volume  discusses  in  greater 
detail  many  of  the  topics  of  this  one,  and  gives  numerous  references 
to  supplementary  material.  A  list  of  books  on  geography  and  related 
subjects  which  might,  well  be  in  a  high  school  library  is  given  at  the 
end  of  this  book. 


CONTENTS 


CHAPTER 
1. 
II. 


The  Nature  of  Geography 
Earth  Relations 

The  Solar  System 

The  Earth  as  a  Planet 

Maps  and  Map  Reading 

Terrestrial  Magnetism 

III.  Relief  Features  of  the  Earth 

Relief  Features  of  the  First  Order    . 
Relief  Features  of  the  Second  Order 
Subordinate  Topographic  Features 
Comparison  of  the  Continents 

IV.  The  Nature  and  Functions  of  the  Atmosphere 

General  Conceptions     .... 

Composition    ...... 

Relations  of  the  Different  Constituents  to  Life 
V.    Climatic  Factors:  Temperature  . 

General  Considerations 

Seasons  ....... 

Relation  of  Temperature  and  Altitude 

Representation  of  Temperature  on  Maps 

Ranges  of  Temperature 
VI.     Climatic  Factors:  Moisture 

Importance  of  Atmospheric  Moisture 

Evaporation  ..... 

Humidity         ..... 
VII.     Climatic  Factors:  Pressure  and  Wind 

Pressure         ..... 

Representation  of  Pressure  on  Maps  and  Charts 

Winds     ..... 

Winds  and  Rainfall 
"^III.    Storms  and  Weather  Forecasting 

Weather  Maps 

Cyclones  and  Anticyclones  . 

Weather  Forecasting    . 

Local  Storms 
IX.    Tropical  Climate 

General  Characteristics  of  Tropical  Climates 

Types  of  Climate  Within  the  Tropics 

The  Future  of  the  Tropics  . 
X.     Types  of  Climate  in  the  Temperate  (Intermediate)  Zones 

General  Characteristics  of  Climates  of  the  Temperate 
Zones        ......... 

Types  of  Climate 

vii 


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GEOLOGY 

ByTHOMAS  C.  Chamberlin  and  Rollin  D.  Salisbury, 
Professors  in  the  University  of  Chicago.  (American 
Science  Series.)     3  vols.     8vo. 

Fol.  I.   Geological  Processes  and  Their  Results. 
Vols.  II  and  III.    Earth  History.     (.Not  sold  separately.) 

A  COLLEGE  TEXT-BOOK  OF   GEOLOGY 

By  Thomas  C.  Chamberlin  and  Rollin  D.  Salisbury. 
(American  Science  Series.)     8vo. 

PHYSIOGRAPHY 

By  R.  D.  Salisbury.     (American  Science  Series.)     8vo. 
The  same.     Briefer  Course.     12mo. 
The  same.     Elementary  Course.     12mo. 

ELEMENTS  OF  GEOGRAPHY 

By  Rollin  D.  Salisbury,  Harlan  H.  Barrows  and 
Walter  S.  Tower,  of  the  Department  of  Geography, 
The  University  of  Chicago.  (American  Science  Series.) 
12mo.  

HENRY  HOLT  AND  COMPANY,  Publishers 
New  York  and  Chicago 


MODERN   GEOGRAPHY 


CHAPTER  I 
THE  NATURE  OF  GEOGRAPHY 

Ancient  and  modern  geography.  Geography  has  been  studied 
since  ancient  times,  for  people  always  have  wanted  to  know  about 
the  earth  on  which  they  lived;  but  the  conception  of  geography  has 
changed  greatly  as  years  have  gone  by.  In  olden  times  it  was  re- 
garded as  a  description  of  the  earth.  It  included  an  account  of 
the  countries  into  which  the  earth  is  divided,  their  physical  features, 
such  as  rivers,  mountains,  and  plains,  and  their  inhabitants  and 
products.  Modern  geography  is  concerned  especially  with  the 
effects  of  physical  features,  such  as  land  forms,  water,  and  cHmate, 
on  living  things. 

Divisions  of  geography.  It  is  clear  that  there  are  two  main 
parts  to  the  study  of  geography:  (i)  The  physical  features  of  the 
earth  (land,  water,  air)  which  afifect  life;  and  (2)  the  ways  in  which 
different  forms  of  life  respond  to  their  physical  surroundings. 

Various  groups  of  physical  phenomena  may  be  the  subjects  of 
special  study.  Thus  the  phenomena  of  the  atmosphere  are  considered 
in  meteorology  and  climatology;  those  of  the  waters  in  oceanography 
and  hydrography;  and  those  of  the  lands  in  physiography,  as  some 
would  define  that  term.  Similarly,  earth  relations  to  life  may  be 
studied  with  special  reference  to  plants  {plant  geography),  to  animals 
{animal  geography),  or  to  man  {human  geography). 

Relations  to  other  subjects.  The  study  of  these  different 
phases  of  geography  brings  it  into  contact  with  many  other  sciences. 
The  form,  size,  and  motions  of  the  earth  are  matters  of  astronomy 
as  well  as  geography;  the  origin  and  characteristics  of  land  forms 
and  the  distribution  of  useful  minerals  are  matters  of  geology  as  well 
as  geography;  the  effects  of  physical  conditions  on  plant  and  animal 


2  THE  NATURE  OF  GEOGRAPHY 

life  are  phases  of  botany  and  zoology  as  v:ell  as  geography;  the  distri- 
bution of  mankind,  man's  subdivision  of  the  earth  into  poUtical 
units,  and  many  other  matters,  relate  geography  closely  to  history; 
and  man's  present  activities,  influenced  by  geographic  conditions, 
are  factors  of  political  economy. 

Importance  of  human  geography.  Most  interest  attaches  to  the 
study  of  the  earth  in  its  relations  to  man.  Human  activities  are  so 
many  and  varied,  and  are  influenced  in  so  many  ways  by  physical 
conditions,  that  special  study  often  is  made  of  related  effects.  Thus 
economic  geography  traces  the  influence  of  natural  factors  in  the  pro- 
duction of  things  useful  to  man.  The  relations  of  land  forms,  soil, 
and  cHmate  to  the  raising  of  crops  is  an  example.  Commercial 
geography  considers  the  influence  of  natural  factors  in  the  transporta- 
tion and  exchange  of  various  commodities,  as  the  trade  in  tropical 
fruits  between  warm  regions  and  those  too  cold  to  raise  them.  His- 
torical geography  is  concerned  with  the  influence  of  physical  condi- 
tions on  past  events.  Political  geography  traces  the  influences  of  lo- 
cation, topography,  climate,  and  natural  resources  on  the  develop- 
ment of  countries. 

The  basis  of  other  studies.  Since  geography  shows  the  many 
ways  in  which  the  earth  is  related  to  the  life  of  man,  it  is  important 
as  the  basis  of  many  other  studies.  It  is  especially  important  in 
connection  with  the  study  of  history,  for  in  all  ages  the  conditions 
under  which  people  lived  have  influenced  their  occupations,  their 
stage  of  development,  and  their  relations  to  the  rest  of  the  world. 
The  better  geography  is  understood,  therefore,  the  easier  it  is  to  under- 
stand the  meaning  of  historical  events.  The  Jews  in  Palestine  never 
became  seamen  because  the  nearest  coast  had  no  good  harbors, 
while  their  neighbors,  the  Phoenicians,  on  a  more  favorable  coast, 
were  the  first  good  sailors,  and  for  many  years  were  influential  in 
Mediterranean  districts  outside  their  own  country.  Russia  has 
striven  for  more  than  two  centuries  to  secure  satisfactory  seacoasts, 
and  as  a  result  has  been  led  into  several  wars  with  her  neighbors. 
Great  Britain,  diflScult  to  invade  because  an  island,  was  able  at 
an  early  date  to  use  her  natural  resources  to  great  advantage,  and 
became  the  leading  nation  of  the  world  in  manufacturing  and  com- 
merce. In  our  country,  slavery  developed  chiefly  in  the  South, 
mainly  because  the  conditions  of  field  labor  there  favored  it  more  than 
in  the  North.  These  examples  suggest  the  close  connection  between 
geography  and  some  important  facts  and  phases  of  history. 


EARTH   CONDITIONS   AND   LIFE  3 

Geography  is  related  no  less  intimately  to  present  events.  The 
distribution  of  people  over  the  face  of  the  earth,  the  manner  in  which 
they  live,  and  their  grouping  in  countries  and  cities  always  bear  some 
relation  to  earth  conditions.  Many  old  cities,  like  Venice,  were 
located  where  defense  against  invasion  was  easy.  Most  new  cities 
were  located  with  respect  to  natural  advantages  for  manufacturing 
or  commerce.  Food,  dress,  shelter,  occupations,  industries,  prod- 
ucts, trade,  and  many  other  facts  and  conditions  of  life  are  in- 
fluenced by  physical  surroundings.  Deserts  have  little  vegetation 
and  few  animals,  for  water  is  scarce.  Since  man  depends  on  plants 
and  animals  for  food  and  clothing,  and  largely  also  for  shelter,  desert 
populations  are  small. 

Tropical  natives  wear  little  clothing  and  eat  little  meat,  largely 
because  bodily  temperatures  are  maintained  easily  without  either. 
They  have  little  commerce,  because  their  wants  are  few.  The 
people  of  middle  latitudes,  on  the  other  hand,  must  adapt  them- 
selves, in  the  matter  of  food,  clothing,  and  shelter,  to  extremes  of 
heat  and  cold.  Their  wants  are  therefore  many  and  varied.  Com- 
plex industries  and  world  commerce  are  needed  to  satisfy  them. 
The  United  States  is  the  greatest  producer  of  foodstuffs,  because  of 
the  great  extent  of  favorable  surface,  soil,  and  climate  —  resources 
which  a  progressive  people  have  used  to  advantage.  Several  coun- 
tries of  western  Europe  have  advantages  for  extensive  manufacturing, 
such  as  supplies  of  coal  near  good  seaports;  but  they  cannot  produce 
all  the  raw  materials  needed  for  their  factories,  nor  all  the  food  for 
their  factory  workers.  Hence  large  quantities  of  raw  materials  and 
food,  like  cotton  and  copper,  flour  and  meat,  are  exported  yearly 
from  the  United  States  to  these  European  countries. 

An  understanding  of  the  larger  relations  between  physical  con- 
ditions and  life  in  general  is  necessary  for  an  understanding  of  the 
effects  of  the  physical  surroundings  of  man  on  his  interests  and 
activities.  This  in  turn  helps  one  to  understand  the  affairs  of  the 
world,  and  therefore  is  important  to  good  citizenship. 


CHAPTER   II 
EARTH    RELATIONS 

The  Solar  System 

Members  of  solar  system.  The  solar  system  includes  the  sun 
and  all  the  bodies  which  revolve  about  it  (Fig.  i).  There  are  eight 
planets,  of  which  the  earth  is  one.  To  us,  all  the  planets  except  our 
own  appear  as  stars,  but  in  their  motions  they  differ  from  other 
stars.     Commencing  with  the  nearest  to  the  sun,  the  planets  are, 


Fig.  I.  Diagram  of  the  principal  members  of  the  solar  system.  The  size 
of  the  bodies  is  exaggerated  greatly  as  compared  with  that  of  the  sun  and  the 
orbits.    The  central  body  is  the  sun;  the  others  are  the  planets. 

in  order:  Mercury,  Venus,  Earth,  Mars,  Jupiter,  Saturn,  Uranus, 
and  Neptune.  All  but  Mercury  and  Venus  have  satellites  correspond- 
ing to  our  moon.     Saturn  has  nine  of  them. 

Besides  the  planets  and  their  satellites,  the  solar  system  includes 
numerous  other  bodies  (mostly  asteroids)  which  have  little  influence 
on  the  earth. 

The  sun  is  more  than  1,000,000  times  as  large  as  the  earth,  and 
very  hot.  From  it  the  earth  receives  nearly  all  its  heat  and  light. 
The  other  planets  shine  only  by  reflected  sunlight. 

Beyond  the  great  system  to  which  the  earth  belongs  there  are 
many  thousands  of  stars,  each  of  which  may  be  compared  to  our 
sun,  though  many  of  them  are  vastly  larger. 

The  planets.  The  planets  are  all  of  similar  form,  all  rotate  on 
axes,  and  move  in  nearly  circular  paths  about  the  sun  in  the  same 
direction,  but  they  are  strikingly  unlike  in  some  respects.    Jupiter, 


THE   FORM   OF   THE   EARTH  5 

the  largest,  has  a  diameter  more  than  ten  times  that  of  the  earth, 
while  the  diameter  of  Mercury,  the  smallest  planet,  is  only  about  one- 
third  that  of  the  earth.  The  innermost  planet  revolves  about  the 
sun  in  88  days,  the  outermost  in  165  years.  The  shortest  rotation 
period  of  a  planet  is  less  than  10  hours,  while  that  of  Venus  is  nearly 
225  days.  From  the  standpoint  of  life,  the  earth  is  the  most  favored 
of  the  planets.  Indeed,  the  conditions  of  heat  and  light  would  prevent 
the  exiitence  of  such  life  as  we  know  on  most  of  the  other  planets. 


The  Earth  as  a  Planet 

Form.  The  form  of  the  earth  is  very  much  like  that  of  a  sphere, 
but  since  it  is  not  exactly  a  sphere,  it  is  called  a  spheroid.  The  form 
has  been  determined  in  various  ways:  (i)  Ships  have  sailed  around 
it.  This  proves  that  it  is  everywhere  bounded  by  curved  surfaces, 
but  it  does  not  prove  that  it  is  a  sphere  or  even  a  spheroid,  for  it  would 
be  possible  to  sail  around  it  if  it  had  the  shape  of  an  egg.  (2)  When 
a  vessel  goes  to  sea,  its  lower  part  disappears  first,  and  when  a  vessel 
approaches  land,  its  highest  part  is  seen  first  from  the  land.  By 
people  on  the  vessel,  the  highest  lands  are  seen  first,  and  the  low 
ones  later;  the  spires  and  chimneys  of  buildings  appear  before  the 
roofs,  and  the  roofs  before  the  lower  parts.  Like  (i)  above,  these 
facts  show  only  that  the  earth  has  a  curved  surface.  But  from 
whatever  port  vessels  start,  and  in  whatever  direction  they  sail, 
objects  on  land  disappear  at  about  the  same  rate.  This  means  that 
the  curvature  of  the  surface  is  nearly  the  same  in  all  directions.  A  body 
whose  curvature  is  the  same  in  all  directions  is  a  sphere,  and  a  body 
whose  curvature  is  nearly  the  same  in  all  directions  is  nearly  a  sphere. 
(3)  Again,  the  earth  is  sometimes  between  the  sun  and  the  moon.  It 
then  casts  a  shadow  on  the  moon  (making  an  eclipse),  and  this  shadow 
always  appears  to  be  circular.  In  these  and  other  ways  it  is  known 
that  the  form  of  the  earth  does  not  depart  greatly  from  that  of  a 
sphere.  (4)  That  the  earth  is  not  exactly  round,  however,  is  shown  in 
various  ways.  For  example,  a  body  weighs  slightly  more  in  high 
latitudes  than  in  low  latitudes.  This  means  that  it  is  nearer  the 
center  of  the  earth  in  the  high  latitudes  than  in  the  low;  or,  in  other 
words,  that  the  earth  is  not  a  true  sphere.  (5)  Certain  mathematical 
calculations  not  given  here  (for  one  of  them,  see  p.  11)  prove  that  the 
curvature  of  the  earth's  surface  is  less  in  high  latitudes  than  nearer 
the  equator. 


6  EARTH   RELATIONS 

Consequences  of  the  earth's  form.  The  spheroidal  form  of  the 
earth  faciUtates  travel  and  transportation.  It  aids  commerce  in 
another  important  way.  The  attraction  of  the  earth  causes  bodies 
to  have  weight.  Because  the  earth  is  nearly  round,  gravity  is  nearly 
equal  everywhere  upon  its  surface,  and,  as  we  have  already  seen,  the 
weight  of  a  given  object  is  therefore  nearly  constant.  If  the  weight 
of  things  varied  greatly  from  place  to  place,  this  variation  would 
interfere  seriously  with  trade  between  different  parts  of  the  world. 

Size.  The  circumference  of  the  earth  is  nearly  25,000  miles, 
and  its  diameter  nearly  8,000  miles.  Since  the  earth  is  not  a  perfect 
sphere,  its  various  diameters  and  circumferences  are  not  exactly 
equal.  Its  longest  diameter  is  7,926.5  miles  and  its  shortest  nearly 
27  miles  less  (7,899.7  miles).  The  area  of  the  earth's  surface  is 
nearly  197,000,000  square  miles. 

Motions 

The  earth  has  two  principal  motions :  ( i )  It  rotates  on  its  shortest 
diameter,  called  its  axis,  and  (2)  it  revolves  around  the  sun.  The 
axis  is  an  imaginary  line,  and  its  ends  are  the  poles.  The  circumfer- 
ence midway  between  the  poles  is  the  equator. 

Rotation.  The  rotation  of  the  earth  from  west  to  east  gives  us 
day  and  night,  for  one  side  of  the  earth  and  then  the  other  is  turned 
toward  the  sun  during  each  rotation.  The  time  of  rotation,  about 
24  hours,  determines  the  length  of  a  day  (day  and  night). 

Human  activities  are  in  general  adjusted  to  the  turning  of  the 
earth,  the  succession  of  daylight  and  darkness  affording  convenient 
intervals  for  work  and  rest.  In  those  parts  of  the  earth  where  the 
intervals  of  light  and  of  darkness  are  many  days  (instead  of  hours), 
this  habit  of  regularity  of  work  and  rest  is  less  general.  During 
the  long  period  of  light,  the  hunting  people  of  Greenland,  for  example, 
cease  their  work  or  seek  rest  only  when  fatigue  overtakes  them. 
During  the  long  period  of  darkness  they  have  no  regular  work  or  exer- 
cise, and  are  much  less  vigorous  than  in  the  period  of  light.  The 
long  "  night "  of  polar  regions  is  very  trying  to  the  health  and  strength 
of  people  accustomed  to  a  period  of  light  each  day. 

The  period  of  rotation  furnishes  also  a  natural  unit  for  measuring 
time.  Again,  the  rising  and  setting  of  the  sun,  due  to  the  earth's 
rotation,  give  us  a  simple  system  of  directions. 

Revolution.  The  earth  revolves  about  the  sun  in  a  little  more 
than  365  days,  and  the  period  of  revolution  fixes  the  length  of  the  year. 


MOTIONS   OF   THE   EARTH  7 

The  path  of  the  earth  around  the  sun  is  its  orbit.  The  orbit  of  the 
earth  is  not  a  circle,  but  a  curve  called  an  ellipse  (Fig.  2),  and  the 
distance  of  the  earth  from  the  sun  varies  from  time  to  time.     When 


Perilieli 


Aplielloa 


Fig.  2.    The  orbit  of  the  earth  is  an  ellipse,  with  the  sun  in  one  of  the  foci. 

the  earth  is  nearest  the  sun  (perihelion),  the  distance  between  them 
is  about  3,000,000  miles  less  than  when  they  are  farthest  apart 


MARCH  SI 


0EC.22 


SEPT.  22 


Fig.  3.    Diagram  showing  the  position  of  the  earth  with  reference  to  the  sun 
at  the  solstices  and  equinoxes,  and  the  inclination  of  its  axis. 


(aphelion).  The  earth  is  nearest  the  sun  (about  91,500,000  miles) 
in  the  early  part  of  the  winter  of  the  northern  hemisphere  (about 
January  ist),  and  farthest  from  it  (about  94,500,000  miles)  early  in 
the  summer.    The  motion  of  the  earth  through  space  during  its 


8 


EARTH   RELATIONS 


revolution  about  the  sun  is  at  the  rate  of  about  600,000,000  miles  a 
year,  or  more  than  1,100  miles  each  minute. 

The  earth's  axis  is  inclined  toward  the  plane  of  its  orbit  about 
23^  degrees  (Fig.  3).  This  position  of  the  axis,  together  with 
the  motions  of  the  earth,  has  much  to  do  with  the  distribution  of 
the  heat  and  light  received  from  the  sun,  with  the  changes  in  the 
length  of  day  (daylight)  and  night,  and  with  the  seasons.^ 

Latitude,  Longitude,  and  Time 

Latitude.  The  equator  has  been  defined  as  the  circle  about 
the  earth  midway  between  the  poles.  Circles  parallel  to  the  equa- 
tor are  parallels.  The  number  of  parallels  which  might  be  drawn 
is  very  large,  though  only  a  few  are  represented  on  maps.  The 
Icxigth  of  parallels  varies  greatly,  those  near  the  equator  being  longer, 


Fig.  4.     Parallels  and  meridians. 


and  those  near  the  poles  shorter.  The  north  and  south  lines  that 
pass  from  pole  to  pole  on  the  earth's  surface  are  meridians.  All 
meridians  come  together  at  each  pole. 

A  few  meridians  and  parallels  appear  in  Fig.  4,  which  shows 
the  earth  in  two  positions.  The  left-hand  part  of  the  figure  shows 
the  half  of  each  parallel  represented  and  the  whole  of  each  meridian. 
The  right-hand  part  shows  the  relation  of  parallels  to  the  North 
Pole.  The  distance  between  the  equator  and  either  pole  is  divided 
into  90  parts,  called  degrees  (written  90°).  Each  degree  is  divided 
into  60  parts,  called  minutes  (60').  Each  minute  is  divided  into 
60  parts,  called  seconds  (60").  Distance  north  or  south  of  the  equa- 
tor may  therefore  be  determined  from  a  globe  or  map  by  means  of 
parallels.  The  system  of  parallels  and  meridians  is  made  possible 
by  the  form  of  the  earth  and  its  rotation  on  its  axis. 


LOCATION  OF  PLACES  ON  THE  EARTH 


Distance  north  or  south  of  the  equator  is  called  latitude.  North 
latitude  is  north  of  the  equator,  and  south  latitude  is  south  of  it.  The 
degrees,  minutes,  and  seconds  are  numbered  from  the  equator  toward 
the  poles.  The  latitude  of  the  equator  is  o°.  Latitude  i°  N.  is  one 
degree  north  of  the  equator,  and  latitude  90°  N.  is  at  the  North  Pole. 
Latitude  1°  S.  is  one  degree 
south  of  the  equator,  and  lati- 
tude 90°  S.  is  at  the  South  Pole. 

Longitude.  Position  on  a 
parallel  is  indicated  by  means 
of  the  meridians  which  cross  it. 
The  number  of  possible  merid- 
ians is  very  great,  but,  as  in 
the  case  of  parallels,  only  a  few 
are  commonly  shown  on  maps. 
One  meridian,  that  passing 
through  Greenwich,  England, 
where  the  British  Royal  Obser- 
vatory was  established  in  1675, 
is  usually  chosen  as  the  merid- 
ian from  which  distances  east 
and  west  are  reckoned  (Fig.  5). 
This  meridian  is  the  meridian 
of  0°,  and  is  sometimes  called 
the  prime  meridian.     Distance 

east  or  west  of  this  meridian  is  known  as  longitude.  Places  east  of 
longitude  0°  are  in  east  longitude,  and  those  west  of  it  are  in  west  longi- 
tude. East  and  west  longitude  respectively  are  regarded  as  extending 
180°  from  the  meridian  of  0°;  that  is,  half-way  around  the  earth. 

The  position  of  a  place  on  the  earth 's  surface  may  be  fixed  exactly 
by  means  of  meridians  and  parallels.  If  a  place  is  in  longitude  30° 
E.,  its  distance  east  of  the  meridian  0°  is  known.  If  at  the  same 
time  it  is  in  latitude  30°  N.,  it  must  be  on  the  parallel  of  30°  N.  where 
it  is  crossed  by  the  meridian  of  30°  E.  So  convenient  and  accurate 
is  this  method  of  locating  places  and  reckoning  distance,  that  parallels 
and  meridians  are  used  in  many  places  as  boundaries  between  states, 
counties,  and  townships. 

The  poles  are  the  only  places  which  have  latitude  but  no  longitude. 
Since  all  meridians  come  together  at  the  poles,  the  poles  cannot  be 
said  to  lie  either  east  or  west  of  the  meridian  of  Greenwich.     At  the 


South 


Fig.  5.  Diagram  showing  the  position 
of  the  axis  of  the  earth,  the  poles,  the 
equator,  the  meridian  of  Greenwich,  and 
the  meridian  of  180°. 


lO 


EARTH   RELATIONS 


North  Pole  the  only  direction  is  south,  and  at  the  South  Pole  the  only 
direction  is  north. 

Longitude  and  time.  There  is  a  definite  relation  between 
longitude  and  time.  Since  the  earth  turns  through  360°  in  24  hours, 
it  turns  15°  in  one  hour,  and  15'  of  longitude  in  one  minute  of  time. 
The  sun  therefore  rises  one  hour  earlier  at  a  place  in  longitude  0° 
than  at  a  place  in  the  same  latitude  in  longitude  15°  W.,  and  one 


Fig.  6.     Map  showing  standard  time  belts  of  the  United  States  in  Dec,  1912. 


hour  later  than  at  a  place  in  the  same  latitude  in  longitude  15°  E. 
Similarly,  noon  comes  an  hour  earlier  in  longitude  0°  than  in  longitude 
15°  W.,  and  an  hour  later  than  in  longitude  15°  E.  All  places  on  a 
given  meridian  have  noon  at  the  same  time  and  midnight  at  the  same 
time,  and  such  places  are  said  to  have  the  same  time;  but  places  on  dif- 
ferent meridians  have  different  times.  St.  Louis  is  about  15°  farther 
west  than  Philadelphia,  and  Denver  is  about  15°  west  of  St.  Louis. 
When  it  is  noon  at  Philadelphia  it  is  about  eleven  o  'clock  at  St.  Louis 
and  ten  at  Denver.  When  it  is  one  o  'clock  at  Philadelphia  it  is  noon 
at  St.  Louis  and  eleven  o'clock  at  Denver,  and  when  it  is  noon  at 
Denver  it  is  one  o  'clock  at  St.  Louis  and  two  at  Philadelphia. 

The  variations  of  time  with  changes  of  longitude  become  apparent 
when  long  journeys  are  made  either  east  or  west.    Thus  a  watch  which 


STANDARD   TIME  BELTS  ii 

has  the  correct  time  in  New  York  has  not  the  correct  time  when  it  is 
carried  to  Chicago.  To  avoid  the  difi&culties  of  time-keeping  growing 
out  of  travel,  the  railroads  of  the  United  States  have  adopted  a  sys- 
tem of  standard  time.  Under  this  system  the  country  is  divided  into 
north-south  belts  of  convenient  width  (Fig.  6),  and  in  each  belt  all 
railways  use  the  same  time.  The  railway  time  in  adjacent  belts 
differs  by  one  hour.  By  this  system,  clocks  and  watches  do  not  show 
correct  local  time  except  on  one  meridian  of  each  belt.  The  irregular 
boundaries  of  the  belts  are  due  to  the  adoption  of  the  nearest  impor- 
tant railway  points  as  the  places  for  changing  time  on  east  and  west 
journeys. 

Lengths  of  degrees.  The  length  of  a  degree  of  longitude,  as 
measured  on  the  surface  of  the  earth,  is  the  ^/z^o  part  of  a  parallel. 
Since  the  parallels  are  very  much  shorter  near  the  poles  than  near 
the  equator,  the  length  of  a  degree  of  longitude  is  less  in  high  than  in 
low  latitudes.  At  the  poles,  where  the  length  of  the  parallel  becomes 
zero,  the  length  of  a  degree  of  longitude  also  becomes  zero.  At  the 
equator,  a  degree  of  longitude  is  a  little  more  than  69  (69.16)  miles. 

Degrees  of  latitude  are  measured  on  meridians.  They  also  vary 
in  length.  The  length  of  a  degree  of  latitude  is  about  68^  miles 
in  India,  while  in  Sweden,  the  most  northerly  place  where  a  degree 
has  been  measured,  it  is  69^^  miles.  All  measurements  which  have 
been  made  show  that  the  length  of  a  degree  of  latitude,  measured 
on  the  earth's  surface,  increases  as  the  poles  are  approached.  At 
the  poles  it  is  calculated  that  it  must  be  about  69^  miles.  In  the 
United  States,  the  average  length  is  about  69  miles.  The  increase 
of  length  of  the  degree  toward  the  poles  means  that  the  earth  is 
flattened  there.    This  means  that  the  earth  is  a  spheroid. 

Inclination  of  Axis  and  its  Effects 

The  sun's  rays  illuminate  one-half  of  the  earth  all  the  time. 
The  border  of  the  illuminated  half  is  called  the  circle  of  illumina- 
tion (Fig.  7).  All  places  on  one  side  of  the  circle  of  illumination  have 
day,  while  all  places  on  the  other  side  have  night.  If  the  axis  about 
which  the  earth  rotates  were  perpendicular  to  the  plane  in  which 
the  earth  revolves  about  the  sun,  the  circle  of  illumination  would 
always  pass  through  the  poles.  Under  these  conditions,  half  of  the 
equator  and  half  of  every  parallel  of  latitude  would  be  illuminated 
all  the  time,  as  in  Fig.  7.  If  the  half  of  each  parallel  were  always 
illuminated,  the  days  and  nights  would  be  equal  everywhere,  for  it 


12 


EARTH   RELATIONS 


takes  just  as  long  for  a  place  at  A  (Fig.  7)  to  move  to  B  (six  hours, 
half  of  a  twelve-hour  day)  as  for  it  to  move  from  B  to  A'  (half  of  a 
twelve-hour  night).  Since  days  and  nights  are  not  equal  at  all  sea- 
sons in  most  parts  of  the  earth,  it  proves  that  the  axis  on  which 

the  earth  rotates  is  not  per- 
pendicular to  the  plane  of 
its  orbit. 

Again,  if  the  earth  rotated 
on  an  axis  perpendicular  to 
the  plane  of  its  orbit,  the 
sun  always  would  be  equally 
high  at  any  given  place  at 
the  same  hour  of  the  day. 
But  this  is  not  the  case.  In 
the  United  States,  for  exam- 
ple, the  sun  is  much  higher 
above  the  horizon  at  noon 
in  summer  than  in  winter. 
The  same  is  true  in  all  lati- 
tudes similar  to  those  of  the 
United  States. 

This  variation  of  the  an- 
gle at  which  the  sun's  rays 
strike  the  same  place  at  dif- 
ferent times,  as  well  as  the  unequal  lengths  of  days  and  nights  in 
most  places,  is  the  result  of  the  inclination  of  the  axis  on  which  the 
earth  rotates  as  it  revolves  around  the  sun  (Fig.  3).  The  position 
of  the  axis  is  constant  throughout  the  year.  The  effect  of  the 
inclination  of  the  axis  is  illustrated  by  Fig.  3,  which  represents  the 
earth  in  four  positions  in  its  orbit.  On  March  21st,  the  half  of  each 
parallel  (the  half  toward  the  reader)  is  illuminated.  At  this  time, 
therefore,  days  and  nights  are  equal  everywhere.  On  June  21st, 
more  than  half  (the  part  not  shaded)  of  every  parallel  of  the  northern 
hemisphere  is  illuminated,  and  there  the  days  are  more  than  1 2  hours 
long  and  the  nights  correspondingly  less.  In  the  southern  hemisphere 
the  nights  are  longer  than  the  days.  On  September  2  2d,  the  days  and 
nights  are  again  equal  everywhere,  for  the  circle  of  illumination 
divides  every  parallel  into  two  equal  parts.  In  the  figure,  the  lighted 
part  is  away  from  the  reader.  On  December  2 2d,  more  than  half  of 
each  parallel  in  the  southern  hemisphere  is  in  the  light,  and  there  the 


90^ 


Fig.  7.  Diagram  to  illustrate  the  fact  that 
half  of  the  earth  is  lighted  by  the  sun  at  any- 
one time.  The  parallel  lines  at  the  right 
show  the  direction  of  the  sun's  rays.  The 
part  of  the  earth  not  shaded  is  lighted  by 
the  sun;  the  other  half  is  in  darkness.  The 
line  between  the  illuminated  half  and  the 
half  which  is  not  illuminated  is  the  circle  of 
illumination.  This  diagram  represents  con- 
ditions at  the  time  of  an  equinox. 


EFFECTS   OF   INCLINATION  OF  EARTH'S   AXIS      13 


Fig.  8. 


days  are  longer  than  the  nights,  while  in  the  northern  hemisphere  the 
nights  are  longer  than  the  days.     Twice  during  the  year,  therefore, 
on  March  21st  and  September  2  2d,  the  days  and  nights  are  equal 
everywhere.    These  times 
are   known   as   the   equi- 
noxes.    The    equinox    in 
March  is  the  vernal  equi- 
nox;   that   in    September 
is  the  autumnal  equinox. 

When  the  earth  is  in 
the  relation  to  the  sun 
shown  in  the  position 
marked  June  21st,  Fig.  3, 
the  days  are  longest  in 
the  northern  hemisphere, 
the  sun  is  highest  in  the 
heavens  at  noon,  and  its 
rays  fall  perpendicularly 
on  the  surface  of  the  earth 
farther  north  (23°  27'+) 
than  at  any  other  time. 
This  is  the  summer  solstice 
(Fig.  8).  The  winter  sol- 
stice occurs  six  months 
later,  when  the  sun 's  rays 
strike  the  earth  vertically 
23^°  (nearly)  south  of 
the  equator  (Fig.  9),  and 
when  the  days  of  the 
southern  hemisphere  are 
longest  and  those  of  the 
northern  shortest.  Figs. 
7,  8,  and  9  also  show  that 
the  days  and  nights  are 
always  equal  at  the  equa- 
tor, since  the  equator  is 
always  bisected  by  the 
circle  of  illumination. 
Days  and  nights  are  not 
always  equal  in  any  other 


Fig.  9. 

Fig.  8.  Diagram  illustrating  the  efifect  of 
inclination  of  the  earth's  axis  on  the  length  of 
day  and  night.  In  the  figure,  more  than  half 
of  every  parallel  of  the  northern  hemisphere  is 
illuminated.  The  days  in  the  northern  hemi- 
sphere are  therefore  more  than  twelve  hours 
long,  since  the  half  of  each  parallel  is  the  meas- 
ure of  180°  of  longitude,  and  180°  of  longitude 
corresponds  to  twelve  hours  of  time.  Similarly 
less  than  half  of  every  parallel  of  the  southern 
hemisphere  is  illuminated,  and  the  days  are 
therefore  less  than  twelve  hours  long. 

Fig.  9.  The  relation  of  the  earth  to  the 
sun's  rays  at  a  time  six  months  later  than  that 
represented  in  Fig.  8.  The  conditions  of  day 
and  night  in  the  hemispheres  are  reversed. 


14 


EARTH   RELATIONS 


Sp&A 


latitude,  unless  at  the  poles,  where  there  is  one  day  (or  period)  of  six 
months  of  light,  and  one  night  (or  period)  of  six  months  of  darkness. 
The  relative  duration  of  daylight  and  darkness,  and  the  angle 
at  which  the  sun 's  rays  strike  the  earth,  are  the  chief  causes  of  changes 
of  seasons.  Thus  at  the  equator,  where  the  hours  of  day  and  night 
are  always  equal,  and  the  sun's  rays  nearly  vertical  at  all  times  of 
the  year,  seasons  differ  but  little,  while  toward  the  poles,  say  in 

Lat.  60°,  where  days  and 
nights  are  very  unequal 
most  of  the  time,  seasons 
differ  greatly. 

It  will  be  seen,  therefore, 
that  most  of  our  methods 
of  reckoning  years,  seasons, 
days,  distances  and  posi- 
tions, weights,  and  direc- 
tions depend  on  the  various 
earth  relations. 

Apparent  motion  of  the 
sun.  The  effect  of  the  in- 
clination of  the  axis  of  the 
earth  is  to  make  the  sun  ap- 
pear to  move  north  and  south 
once  during  each  revolution  of  the  earth  about  the  sun.  That  is, 
the  revolution  of  the  earth  about  the  sun,  while  it  rotates  on  an  in- 
clined axis,  makes  the  sun  appear  to  move  from  a  place  where  its  rays 
are  vertical  23J^°  (nearly)  north  of  the  equator  (direction  S,  Fig.  10), 
to  a  place  where  they  are  vertical  23^^°  (nearly)  south  of  the  equator 
(direction  W),  and  back  again,  in  one  year.  The  result,  so  far  as  the 
earth  is  concerned,  is  as  if  the  sun  moved  from  S,  which  corresponds 
to  the  time  of  the  summer  solstice,  to  Sp  b°  A,  which  corresponds 
to  the  time  of  the  autumn  equinox,  then  to  W,  which  corresponds  to 
the  time  of  the  winter  solstice,  then  back  again  to  Sp  b'  A,  which 
corresponds  to  the  spring  equinox,  and  finally  to  S,  while  the  earth 
is  making  one  circuit  about  the  sun. 

When  the  sun  is  vertical  at  points  north  of  the  equator,  the  days 
are  longer  than  the  nights  in  the  northern  hemisphere,  and  the  sun 's 
rays  strike  the  surface  in  the  northern  hemisphere  more  nearly  ver- 
tically than  they  do  in  the  southern  hemisphere.  The  greater  number 
of  hours  of  sunshine  and  the  more  nearly  vertical  rays  explain  the 


Fig.  10.     Diagram  illustrating  the  appar- 
ent motion  of  the  sun. 


MAPS  AND    MAP  READING  15 

warmth  of  our  summer,  even  though  the  earth  is  then  farthest  from 
the  Sim.  In  high  latitudes,  as  in  western  Canada,  the  long  period  of 
sunlight  (16  to  18  hours)  is  an  important  factor  in  the  successful 
cultivation  of  crops,  in  spite  of  the  short  summer.  When  the  sun  is 
vertical  at  the  equator,  days  and  nights  are  equal  everywhere,  and 
when  the  sun  is  vertical  south  of  the  equator,  days  are  longer  than 
nights  in  the  southern  hemisphere,  and  the  sun 's  rays  are  more  nearly 
vertical  there  than  in  the  northern  hemisphere. 

The  northernmost  parallel  where  the  sun's  rays  are  ever  vertical 
is  called  the  tropic  of  Cancer.  The  corresponding  southernmost 
parallel  is  the  tropic  of  Capricorn.  The  tropics  are  nearly  23^^° 
(23°  27'+)  from  the  equator,  because  the  axis  of  the  earth  is  inclined  by 
that  amount  toward  the  plane  of  its  orbit.  The  sun  is  vertical  at  the 
tropic  of  Cancer  at  the  time  of  the  summer  solstice,  and  at  the  tropic 
of  Capricorn  at  the  time  of  the  winter  solstice.  The  parallels  just 
touched  by  the  circle  of  illumination  at  the  time  of  the  solstices  are 
the  polar  circles.  They  are  as  far  from  the  poles  as  the  tropics  are 
from  the  equator.  They  are  therefore  in  latitude  about  66^°. 
The  one  in  north  latitude  is  the  Arctic  circle,  and  the  one  in  south 
latitude  is  the  Antarctic  circle. 

Within  the  polar  circles  the  differences  of  the  seasons  are  chiefly 
a  matter  of  daylight  and  darkness.  Between  ^lxp^■  tropics  there  are 
no  changes  of  seasons  like  those  of  the  United  Staves.  Hence  it  is 
only  between  the  polar  circles  and  the  tropics  that  there  are  four 
seasons  of  the  year,  to  be  called  truly  spring,  summer,  autumn,  and 
winter. 

Maps  and  Map  Reading 

What  is  known  of  the  earth 's  surface  may  be  represented  in  vari- 
ous ways  — by  globes,  models,  and  maps.  Globes  have  the  great 
advantage  of  showing  without  distortion  the  distribution  of  land  and 
sea,  and  other  large  surface  features.  It  is  not  practicable,  however, 
to  make  them  large  enough  to  show  minor  features,  and,  even  apart 
from  this,  they  are  not  suited  to  all  purposes.  Models,  or  reHef  maps, 
reproduce  on  a  small  scale  the  unevenness  of  the  earth's  surface.  In 
order  that  the  elevations  may  stand  out  clearly,  their  height  is  exag- 
gerated greatly  on  most  models,  which  are  likely,  therefore,  to  give 
false  impressions. 

Map  projections.  The  necessity  of  representing  part  or  all  of  the 
earth  on  a  flat  surface  led  very  early  to  the  making  of  crude  maps. 


i6 


EARTH   RELATIONS 


Fig.  II.     Map  representing  relief  by 
hachures.     (U.  S.  Geol.  Surv.) 


It  is,  of  course,  impossible  to  show  the  rounded  surface  of  the  earth 
on  a  flat  surface  without  exaggerating  or  reducing  certain  parts, 
so  that  each  of  the  many  methods  {projections)  devised  from  time 

to  time  for  representing  the 
meridians  and  parallels  of  a 
globe  on  a  plane  surface, 
involves  more  or  less  distor- 
tion. 

Almost  all  sailing  charts  and 
many  maps  of  the  entire  world 
are  made  on  Mercator's  projec- 
tion (Fig.  39),  named  for  the 
inventor.  A  map  on  Merca- 
tor's  projection  is  accurate  at 
the  equator,  but  exaggerates 
areas  more  and  more  as  the 
poles  are  approached.  Thus 
Greenland  (Fig.  39)  appears  to 
be  about  half  as  large  as  North 
America  on  a  Mercator's  map, 
while  in  reality  it  is  less  than  one-fifteenth  as  large. 

Representation  of  relief  on  maps.  The  surface  of  the  land 
is  uneven,  and  it  is  a  matter  of  importance,  in  many  cases,  to  show  the 
unevennesses  {relief)  on  maps.  This  is  done  in  various  ways.  One 
method  is  by  shading  —different  colors  or  shades  representing 
different  elevations  (see  maps  at  end  of  book).  Another  method  is 
by  hachures  (Fig.  11) — lines  drawn  in  the  direction  in  which  the 
land  slopes.  Where  slopes  are  steep,  the  lines  are  made  short  and 
heavy;  where  gentle,  longer  and  lighter.  Such  maps  give  only  a 
general  idea  of  the  form  of  the  land. 

Much  more  exact  information  may  be  had  from  contour-line 
maps.  In  order  to  read  contour-line  maps,  it  is  necessary  to  know 
that  contours  are  lines  drawn  on  maps  to  express  relief,  and  that  any 
given  line  runs  through  points  of  the  same  elevation  above  sea-level. 
This  will  be  understood  readily  by  reference  to  Figs.  12  and  13. 
Fig.  12  shows  a  model  of  an  ideal  landscape  viewed  from  above,  on 
which  lines  have  been  drawn  connecting  places  of  equal  elevation. 
In  Fig.  13  the  above  lines  are  shown  alone;  this  is  a  contour  map 
of  the  region  represented  by  the  model.  By  comparison  of  the  model 
and  map  it  will  be  seen  that  where  the  slopes  of  the  former  are  steep 


WAYS  OF  REPRESENTING  RELIEF  ON  MAPS 


17 


the  lines  of  the  latter  are  dose  together,  and  vice  versa.  The  vertical 
distance  between  two  adjacent  contour  lines  is  the  contour  interval. 
The  contour  interval  varies  on  different  maps.     In  regions  of  low 


Fig.  12.     Model  of  ideal  landscape.     (Keeler.) 


Fig.  13.     Contour  map  of  the  area  shown  in  Fig.  12.  (U.  S.  Geol.  Surv.) 


relief  an  interval  of  10  or  20  feet  generally  is  used;  in  mountainous 
areas  an  interval  of  500  or  more  feet  has  to  be  used  in  some  cases  in 
order  to  avoid  having  the  lines  too  close  together  to  be  read.  In 
the  map  of  Fig.  13,  the  interval  is  20  feet,  the  exact  value  of  the  100 


1 8  EARTH   RELATIONS 

and  200  foot  lines  being  indicated.  By  counting  the  lines  it  will 
be  seen  that  the  top  of  the  hill  to  the  left  of  the  river  is  more  than 
260  feet  above  the  level  of  the  ocean  in  the  foreground.  It  cannot  be 
280  feet  high,  however,  for  no  280  foot  line  is  drawn.  A  comparison 
of  the  model  and  map  will  show  also  how  valley  depressions  are  repre- 
sented by  contours. 

Terrestrial  Magnetism 

The  earth  is  a  great  magnet,  and,  like  the  small  magnets  with  which  we  are 
familiar,  has  two  poles.  One  of  these  poles  is  called  the  North  Magnetic  Pole  and  the 
other  the  South  Magnetic  Pole.  One  end  of  the  compass  needle  points  toward  one 
of  these  poles,  and  the  other  toward  the  other.  If  we  were  to  follow  the  directions 
pointed  by  the  compass  needle,  we  would  be  led  to  the  North  Magnetic  Pole  in  the 
one  case  and  to  the  South  Magnetic  Pole  in  the  other. 

The  magnetic  poles  are  far  from  the  geographic  poles,  the  true  north  and  south 
points,  and  they  are  not  exactly  opposite  each  other.  Their  positions  appear  to 
shift  a  little  from  year  to  year,  but  the  change  is  not  known  to  be  great.  The 
North  Magnetic  Pole  is  in  latitude  about  70°  N.,  and  in  longitude  97°  or  98°  W., 
while  the  South  Magnetic  Pole  is  in  latitude  72°  25'  S.,  and  longitude  155°  16'  E. 

Questions 

1 .  The  horizon  of  a  given  observer  increases  as  he  rises.  What  does  this  prove 
concerning  the  shape  of  the  earth's  surface  at  that  place?  What  further  inference 
could  be  made  from  the  fact  that  as  he  ascends  his  horizon  remains  circular? 

2.  At  places  east  of  a  given  point  the  sun  rises  and  sets  before  it  does  at  that 
point.  At  places  toward  the  west  it  rises  and  sets  after  it  does  at  the  station  in 
question.    What  does  this  indicate  as  to  the  surface  of  the  earth? 

3.  Why  do  the  sun's  rays  never  fall  vertically  in  latitudes  higher  than  23^^°? 

4.  Certain  crops  are  said  to  mature  faster  in  western  Canada  than  farther 
south  in  the  United  States.     Suggest  a  logical  reason  for  this. 

5.  How  would  the  seasons  at  Chicago  (42°  N.)  be  changed  if  the  axis  of  the 
earth  were  inclined  45°,  rotation  remaining  as  now? 

6.  Two  cities  about  690  miles  apart,  on  the  same  meridian,  are  located  in 
latitude  42°  N.  and  3 2°  N. ,  respectively.  From  these  facts  determine  approximately 
the  circumference  of  the  earth. 

7.  What  is  the  difference  in  longitude  of  two  places  having  a  difference  in 
time  of  six  and  one-half  hours? 

8.  What  is  the  difference  in  local  time  between  New  York  City  (74°  W.)  and 
Chicago  (87°  36'  W.)? 

9:  The  altitude  of  the  sun  at  a  given  place  at  noon  at  the  time  of  equinox 
is  50°.     What  is  the  latitude  of  the  place? 

10.  In  what  latitudes  is  the  altitude  of  the  sun  20°  at  noon  at  the  time  of  equinox? 

11.  In  what  latitudes  has  the  sun  a  noon  altitude  of  30°  at  the  time  of  the 
summer  solstice? 

12.  What  is  the  altitude  of  the  sun  at  the  equator  at  noon  at  the  time  of  the 
summer  solstice? 


CHAPTER  III 
RELIEF   FEATURES   OF  THE  EARTH 

The  surface  of  the  land  is  uneven.  The  lowest  lands  are  below 
sea-level,  and  the  highest  point  (Mt.  Everest,  in  the  Himalaya  Moun- 
tains) is  more  than  five  and  one-half  miles  above  sea-level.  The 
relief  of  the  land  surface  is  therefore  not  far  from  six  miles.  Com- 
pared with  the  diameter  of  the  earth,  even  the  loftiest  mountains  are 
slight  elevations,  for  the  height  of  Mt.  Everest  above  the  sea  is  equal 
to  only  V1436  part  of  the  polar  diameter  of  the  earth.  On  a  globe 
10  feet  in  diameter  this  would  correspond  to  one-twelfth  of  an  inch. 

The  sea  bottom  also  is  uneven,  and  its  relief  is  a  little  greater  than 
that  of  the  land.  Since  the  highest  points  of  land  are  nearly  six  miles 
above  the  sea,  and  the  lowest  parts  of  the  sea  bottom  about  six  miles 
below,  the  relief  of  the  surface  of  the  solid  part  of  the  earth  (lithosphere) 
is  almost  twelve  miles.  If  its  surface  were  even,  the  water  of  the  ocean 
would  cover  the  whole  earth  to  the  depth  of  about  9,000  feet. 


Relief  Features  of  the  First  Order 

Continents  and  ocean  basins.  The  average  elevation  of  the 
lands  above  sea-level  is  a  little  less  than  half  a  mile,  while  the  average 
depth  of  the  oceans  is  about  two  and  one-half  miles.  Were  the  height 
of  lands  in  middle  and  high  latitudes  equal  to  the  average  depth  of  the 


Platca 


Mouniains- 


Fig.  14.  Diagram  to  show  the  distinction  between  an  elevated  continental 
area  and  an  ocean  basin.  The  steep  slope  (much  exaggerated)  at  the  left  of  the 
ocean  basin  is  the  line  of  contact  between  the  two,  and  is  the  real  border  of  the 
continental  area.  The  ocean  covers  the  lower  part  of  the  continental  tract, 
namely,  the  continental  shelf.  The  diagram  also  shows  the  general  relation 
between  low  mountains,  such  as  the  Appalachians,  a  low  plateau,  and  a  coastaJ 
plain.    The  continental  shelf  is  a  continuation  of  the  coastal  plain. 

IQ 


20 


RELIEF   FEATURES   OF  THE   EARTH 


oceans,  much  of  each  continent  would  be  too  high  and  cold  to  support 
a  dense  population.  The  continents  and  the  ocean  basins  are  relief 
features  of  the  first  order. 

The  oceans  have  an  area  (143,000,000  square  miles)  more  than  two 
and  one-half  times  as  great  as  that  of  the  lands  (54,000,000  square 
miles).  About  most  continental  borders,  the  water  is  shallow  (less  than 
600  feet)  for  some  miles.  The  bottom  beneath  this  shallow  water  is  the 
continental  shelf  (Fig.  14).  At  their  sea-ward  edges,  the  continental 
shelves  descend,  by  rather  steep  slopes,  to  the  ocean  basins.  Por- 
tions of  the  continental  shelves  have  been  built  up  from  deeper  water 
by  the  deposition  of  sediments  washed  down  from  the  land;  other 
parts  are  due  to  the  sinking  of  former  land  areas;  and  still  others  are 
the  result  of  the  wearing  back  of  the  land  by  waves. 

Many  islands  stand  on  the  continental  shelves,  and  represent  higher  areas 
whose  lower  surroundings  have  sunk,  or  been  cut  by  waves,  below  sea-level.  In 
many  cases  a  slight  elevation  of  the  continental  shelf,  or  a  slight  lowering  of  the 
sea,  would  join  these  islands  to  the  mainland.  Thus  a  rise  of  300  feet  would  trans- 
form most  of  the  area  of  the  Baltic  and  North  seas  into  land,  and  unite  Great 
Britain  with  the  continent.  Such  a  change  would  modify  greatly  conditions  in 
Great  Britain.  Separation  from  the  continent  has  freed  the  United  Kingdom  from 
the  need  of  a  large  standing  army,  and  favored  the  development  of  extensive  sea 
interests,  which  required  the  maintenance  of  a  large  navy  to  protect  them. 

Most  islands  of  the  ocean  outside  the  continental  shelves  are 
volcanic  cones,  or  coral  islands  associated  with  them.  Their  combined 
area  is  only  about  three-fourths  that  of  the  state  of  Illinois. 


Fig.  15.     Land  and  water  hemispheres. 

Grouping  of  the  continents.      The  northern  hemisphere  con- 
tains more  than  twice  as  much  land  as  the  southern.     If  the  earth  be 


PLAINS,  PLATEAUS,  AND   MOUNTAINS  2i 

divided  into  two  hemispheres,  one  with  its  center  in  England  and 
the  other  in  New  Zealand  (Fig,  15),  the  first  would  contain  about 
six-sevenths  of  all  the  land,  and  might  be  called  the  land  hemi- 
sphere, while  the  other  would  contain  only  about  one-seventh  of 
the  land,  and  might  be  called  the  water  hemisphere.  Even  in  the 
land  hemisphere,  however,  the  water  would  cover  rather  more 
than  half  the  surface,  while  in  the  water  hemisphere  it  would  cover 
about  fourteen-fifteenths  of  it.  Since  the  northern  hemisphere 
contains  two-thirds  of  the  land,  and  a  still  larger  proportion  of 
the  productive  land,  it  has  always  supported  a  vast  majority  of  the 
human  race. 


Relief  Features  of  the  Second  Order 

The  more  strongly  marked  features  of  the  continents  and  of  the 
ocean  basins  are  relief  features  of  the  second  order.  The  continental 
areas  are  made  up  of  plains,  plateaus,  and  mountains.  Some  of  their 
relations  are  shown  in  Fig.  14. 

Plains.  Plains  are  the  lowlands  of  the  earth.  They  may  be  but  a 
few  feet  above  the  sea,  or  they  may  be  hundreds  or  thousands  of  feet 
above  it;  but  if  so  high  as  a  thousand  feet,  they  are  in  most  cases  far 
from  the  sea,  and  distinctly  lower  than  some  of  the  other  lands  about 
them.  Plains  differ  widely  among  themselves,  not  only  in  height, 
but  in  position,  size,  shape  of  surface,  fertility,  origin,  and  in  various 
other  ways.  Different  names  are  given  to  various  sorts  of  plains,  the 
names  being  intended  to  call  attention  to  some  one  feature.  Coastal 
plains  border  the  sea,  and  interior  plains  are  far  from  it,  or  are  separat- 
ed from  it  by  high  lands.  The  plains  of  the  Atlantic  and  Gulf  coasts 
illustrate  the  first  class,  while  a  large  part  of  the  area  between  the 
Appalachian  Mountains  and  the  Rocky  Mountains  is  a  great  interior 
plain  (Plate  i). 

Plateaus.  Plateaus  are  highlands  with  considerable  summit  areas; 
but  no  great  elevation  is  necessary  to  make  a  flattish  area  of  land  a 
plateau.  In  general,  a  plateau  is. so  situated  as  to  appear  high  from 
at  least  one  side.  Thus  if  a  coastal  plain  rises  gradually  from  the  sea 
to  a  height  of  200  feet,  and  then  rises  by  a  steeper  slope  to  another 
broad  tract  of  land  which  stands  200  feet  higher  (Fig.  14),  the  upper 
tract  would  be  called  a  plateau.  The  Piedmont  Plateau,  which  lies 
between  the  Appalachian  Mountains  and  the  Atlantic  Coastal 
Plain,  is  not  very  high,  but  it  is  enough  higher  than  the  Coastal 


22  RELIEF   FEATURES   OF   THE   EARTH 

Plain  to  be  distinctly  set  ofif  from  it.  A  large  part  of  this  plateau 
is,  however,  not  so  high  as  much  of  the  great  interior  plain  of  the 
continent. 

Some  plateaus  lie  between  mountains  on  the  one  hand  and  plains 
on  the  other,  as  in  the  case  of  the  Piedmont  Plateau.  Others  lie  be- 
tween mountains,  as  the  plateaus  of  central  Asia  (Fig.  i6),  Mexico, 

Caucasus  Mrs,  Htmalaya  Mta.  Nar-Shan  Mis. 


Fig.  1 6.     Section  across  Asia,  showing  plateau  between  the  Himalayas  and  the 
Nan-Shan  Mountains. 

Sferra  '^Z'"  '^"^''^ 


Fig.  17.  Section  across  North  America,  showing  plateaus  between  the  moun- 
tains in  the  western  part. 

and  western  United  States  (Fig.  17).  Other  plateaus  rise  directly 
from  the  sea,  as  Greenland  and  parts  of  Africa.  The  total  area  of 
plateaus  is  great,  though  less  than  that  of  plains. 

Mountains.  Mountains  are  conspicuously  high  lands  with  slight 
summit  areas  (Fig.  18).     The  tops  of  the  loftiest  mountains  are  be- 

"  tween  five  and  six  miles  above  the  sea,  but  most  mountains  are  not 
half  so  high.  The  highest  mountains  tower  above  any  plateaus, 
but  many  mountains  are  lower  than  the  highest  plateaus.  Few 
mountains  reach  the  height  of  the  Plateau  of  Tibet,  15,000  to  16,000 
feet. 

Mountains  are  unlike  plateaus  of  similar  elevation  in  having  little 
area  at  the  top.     In  the  case  of  mountain  peaks,  this  is  shown  by 

_  the  name.  A  mountain  ridge  may  be  long,  but  in  most  cases  its  top 
is  narrow.  Numerous  peaks  or  ranges  near  together  make  a  moun- 
tain group  or  chain;  but  even  in  great  mountain  groups  there  is  no 
large  expanse  of  land  at  the  summit  level. 

Where  mountains  rise  abruptly  to  great  heights  above  their  surroundings,  they 
are  the  most  impressive  and  awe-inspiring  features  of  the  earth.  In  not  a  few 
cases  they  rise  from  low,  v/arm  plains  to  such  heights  that  their  siunmits  always 
are  covered  with  snow.  Nowhere  else  are  such  extremes  of  climate  found  so  close 
together. 


MINOR  TOPOGRAPHIC  FEATURES 


23 


Mountains  are  the  third  of  the  three  topographic  types  of  the 
second  order,  as  they  appear  on  the  lands  of  the  earth.  In  this  group- 
ing of  mountains,  only  great  groups  or  systems  of  mountains,  such  as 
the  Appalachians,  the  Rockies,  the  Alps,  the  Himalayas,  and  the 
Andes,  are  considered. 

Most  mountain  ranges  are  situated  near  the  edges,  rather  than  in 
the  interiors,  of  the  land  masses,  and  most  of  the  loftier  mountain 
chains  are  not  far  from  the  shores  of  the  greatest  ocean.     The  conti- 


Fig.  18.     Mountains  rising  conspicuously  above  a  plain.     Southern  California. 

nental  slopes  to  the  Pacific  Ocean  are  therefore  shorter  and  steeper 
than  those  to  the  Atlantic  and  Arctic  oceans.  About  one-third  of 
the  land  drains  to  the  Atlantic  Ocean,  one-sixth  to  the  Arctic,  one- 
seventh  to  the  Pacific,  and  one-eighth  to  the  Indian.  The  drainage 
of  the  rest  of  the  land  (22%)  fails  to  reach  the  sea,  and  is  lost  in 
dry  interior  basins. 


Subordinate  Topographic  Features 

The  surfaces  of  most  plains  and  plateaus  are  uneven,  while  the 
very  name  of  mountain  suggests  ruggedness.  Irregularities  of  surface 
consist  of  elevations,  such  as  ridges  and  hills,  above  the  general  level, 
and  of  depressions,  such  as  valleys  and  basins  (depressions  without 
outlets) ,  below  it.  The  elevations  and  the  depressions  are  bordered  by 
slopes,  which,  when  very  steep,  are  called  cliffs.  Ridges,  hills,  valleys, 
basins,  flats,  and  cliffs  affect  mountains,  plateaus,  and  plains;  but  in 
most  cases  they  are  more  pronounced  in  mountains  and  plateaus  than 


24  RELIEF   FEATURES   OF  THE   EARTH 

on  plains.  These  minor  unevennesses  of  surface  are  topographic 
features  of  the  third  order.  The  key  to  their  history  is  found  in  changes 
now  taking  place  on  the  land  (Chapter  XV),  or  in  those  which  have 
taken  place  in  recent  times. 


Comparison  of  the  Continents 

The  position,  form,  size,  and  general  relief  of  the  continents  are 
of  fundamental  importance,  since  these  things  determine,  in  large 
measure,  their  fitness  for  human  occupation.  Europe  (Plate  IV), 
the  smallest  continent  except  Australia,  lies  almost  entirely  in  the 
north  temperate  zone.  It  widens  rapidly  toward  the  south,  so  that 
its  east  and  west  extent  along  the  line  of  the  Mediterranean,  Black, 
and  Caspian  seas  is  nearly  three  times  that  along  the  Arctic  Ocean. 
No  other  continent  has  an  outline  so  irregular.  Great  arms  of  the 
sea  extend  far  inland,  modifying  climate  and  helping  commerce  by 
bringing  most  parts  of  the  continent  into  close  contact  with  the  sea. 
More  than  half  of  Europe  is  less  than  600  feet  above  sea-level,  and 
only  one-sixth  is  over  1,500  feet.  Many  rivers  serve  as  natural  high- 
ways into  the  interior.  Some  of  those  in  the  west  are  unfrozen 
throughout  the  year.  Europe  has  no  tropical  section,  and  no  dry 
desert. 

Asia  (Plate  V),  the  largest  of  the  continents,  is  nearly  4>^  times  the 
size  of  Europe,  and  nearly  5^^  times  as  large  as  the  United  States. 
It  extends  somewhat  farther  north  than  Europe,  and  much  nearer 
the  equator.  Less  than  one-fourth  of  Asia  is  below  600  feet  above  the 
sea,  and  about  one-sixth  is  above  6,000  feet.  The  average  elevation 
is  nearly  three  times  that  of  Europe.  A  central  region  of  high  pla- 
teaus and  mountains  receives  little  rain,  and  is  of  slight  value  to  man. 
The  longest  drainage  slopes  are  toward  the  Arctic.  Because  of  these 
things,  one-half  of  Asia  is  relatively  inaccessible.  Asia  has  only 
about  one-third  as  long  a  coast-line  as  Europe  in  proportion  to  its 
area.  Its  great  size  and  relatively  compact  form  make  it  the  conti- 
nent of  climatic  extremes.  From  a  physical  standpoint  Europe  and 
Asia  form  one  continent  (called  Eurasia),  but  for  historical  and  other 
reasons  they  usually  are  separated. 

Australia  (Plate  VII)  is  only  a  little  larger  than  the  LTnited 
States,  and  is  divided  almost  in  halves  by  the  tropic  of  Capricorn. 
The  coast,  though  less  regular  than  that  of  Africa  and  South  America, 
has  few  harbors  compared  to  Europe  and  North  America.     Because 


THE   CONTINENTS   COMPARED  25 

of  its  position,  size,  compactness,  and  topography,  much  of  Australia 
is  arid  (p.  106).     Australia  is  the  most  isolated  of  the  continents. 

About  two-thirds  of  Africa  (Plate  VI)  are  within  the  tropics. 
Broadly  speaking,  the  continent  consists  of  a  great  plateau,  bordered 
in  places  by  a  narrow  coastal  plain.  At  the  south,  the  plateau  is 
3,000  to  5,000  feet  above  sea-level;  at  the  north,  1,000  to  2,000  feet. 
Only  one-eighth  of  the  land  (less  than  in  any  other  continent)  is  below 
an  elevation  of  600  feet.  The  rivers  descend  in  rapids  or  falls  to  the 
coastal  lowlands.  More  than  one-third  of  the  continent  is  desert, 
while  other  large  areas  are  semi-arid.  Africa  has  the  most  regular 
coast  of  any  continent.  Europe,  with  the  most  irregular  outline, 
has  more  than  six  times  as  much  shore-line  as  Africa,  in  proportion 
to  its  area.  Although  one  of  the  most  ancient  civilizations  had  its 
seat  in  Egypt,  Africa  has  remained  to  our  own  day  the  "dark  conti- 
nent." The  conditions  indicated  above  have  helped  greatly  to 
bring  this  about.  The  fact  that  much  of  the  coast  is  without 
harbors,  and  that  navigation  of  even  the  larger  rivers  is  interrupted 
near  their  mouths  by  falls  and  rapids,  delayed  exploration,  conquest, 
and  commerce.  Both  the  vast  deserts  and  the  dense  equatorial  forests 
retarded  native  progress,  and  discouraged  European  settlement. 

Like  Africa,  South  America  (Plate  III)  is  largely  within  the  tropics 
and  is  very  compact,  with  few  great  indentations,  peninsulas,  or  is- 
lands. On  the  other  hand,  the  proportion  of  desert  is  much  less,  and 
of  lowlands  much  greater.  Two-fifths  of  South  America  are  below 
600  feet,  and  two-thirds  under  1,500  feet. 

In  North  America  (Plate  I),  as  in  Europe,  most  of  the  land  is  in 
middle  latitudes.  Unlike  Europe,  North  America  presents  its  greatest 
width  to  the  cold  polar  seas.  North  America  ranks  next  to  Europe 
and  South  America  in  the  relative  extent  of  its  lowlands.  Nearly 
one-third  of  the  continent  is  below  600  feet,  and  nearly  two-thirds 
below  1,500  feet.  The  vast  interior  plain  stretching  from  the  Arctic 
Ocean  to  the  Gulf  of  Mexico  has  an  unequaled  system  of  navigable 
waterways.  Except  Europe,  North  America  has  the  longest  shore- 
line in  proportion  to  its  size.  The  greatest  indentation,  the  Gulf  of 
Mexico,  affects  the  climate  of  eastern  United  States  profoundly 
(p.  85).  Except  in  the  far  north,  most  of  the  indentations  have 
commercial  importance. 


26  RELIEF   FEATURES   OF  THE   EARTH 


Questions 

1.  South  America  and  Africa  have  few  islands  about  their  borders.  What 
does  this  suggest  concerning  the  width  of  their  continental  shelves?  Does  it 
Prove  anything  about  the  width? 

2.  Soundings  along  the  eastern  coast  of  the  United  States  have  shown  that 
depressions  like  river  valleys  extend  across  the  continental  shelf  from  the  mouths 
of  various  rivers.  What  do  such  depressions  suggest  concerning  the  history  of  those 
parts  of  the  continental  shelf  where  they  occur? 

3.  From  the  comparison  of  the  continents  given  on  pages  24-25,  which  ones 
appear  best  fitted  to  contain  the  most  advanced  nations?  Which  ones  seem 
least  fitted  to  do  so? 

4.  Most  people  live  on  plains.  Would  it  therefore  be  better,  from  the  human 
standooint,  if  the  earth  were  without  mountains?     Reasons? 


CHAPTER  IV 
THE   NATURE  AND   FUNCTIONS   OF  THE  ATMOSPHERE 

General  Conceptions 

Relation  to  rest  of  earth.  Air  is  essential  to  the  life  of  the  earth, 
and  to  most  processes  in  operation  on  the  earth's  surface.  It  helps 
to  distribute  moisture,  it  makes  the  extremes  of  heat  and  cold  less  than 
they  would  be  if  it  did  not  exist,  and  it  is  a  leading  factor  in  the 
formation  of  soil.  Furthermore,  the  atmosphere  is  not  merely  an 
envelope  of  the  rest  of  the  earth,  for  it  goes  down  into  the  soil  and 
rocks  as  far  as  there  are  holes  and  cracks,  and  its  constituents  are 
dissolved  in  the  waters  of  sea  and  land. 

Weight  of  air.  When  the  atmosphere  is  still,  we  are  hardly 
conscious  of  its  existence,  but  many  familiar  phenomena  show  that 
air  is  very  substantial.  Thus  wind,  which  is  only  air  in  motion,  may 
be  so  strong  that  trees  and  buildings  are  blown  down  by  it.  A  wind 
blowing  30  miles  an  hour  exerts  a  force  of  nearly  60,000  pounds  on 
the  side  of  a  house  60  feet  long  and  20  feet  to  the  eaves.  The  pressure 
of  still  air,  that  is,  its  weight,  is  nearly  15  (14.7)  pounds  on  every 
square  inch  of  surface  at  sea-level.  In  other  words,  its  weight  is 
equal  to  that  of  a  layer  of  water  completely  covering  the  earth  to  a 
depth  of  33  feet. 

Density.  The  atmosphere  is  made  up  of  gases.  The  particles 
of  which  the  air  is  composed  are  nearer  together  at  low  altitudes  than 
at  high  altitudes.  At  its  bottom,  the  air  is  pressed  down  by  all  the 
air  above;  at  the  height  of  1,000  feet  the  air  is  pressed  down  by  all 
above  that  level,  and  so  on.  Hence  the  lowest  air  is  under  most 
pressure  and  is  densest.  One-half  the  atmosphere  (by  weight)  lies 
below  a  plane  about  3.6  miles  above  sea-level,  and  three-fourths  of  it 
below  a  plane  6.8  miles  above  the  same  level.  Nearly  three-fourths 
of  the  atmosphere  lies  below  the  top  of  the  highest  mountain.  It 
is  partly  because  the  air  is  less  dense  at  high  levels  that  mountain- 
climbing  is  difficult.  The  body  is  not  accustomed  to  the  lessened 
pressure,  and  it  causes  discomfort. 

27 


28    NATURE  AND  FUNCTIONS  OF  THE  ATMOSPHERE 


Height.  The  actual  height  of  the  atmosphere  is  not  known, 
though  something  is  known  about  it  (Fig.  19). 

(i)  The  greatest  altitude  reached  by  any  mountain-climber  is 
about  24,000  feet.  This  shows  that  the  air  extends  to  a  height  of 
more  than  four  and  one-half  miles. 

(2)  Men  have  gone  up  more  than  six  miles  in  balloons.  In  some 
cases,  the  men  in  the  balloons  became  unconscious  before  this  height 
was  reached,  and  in  other  cases,  where  oxygen  was  carried  for  breath- 
ing, the  chief  discomfort  was  from  cold.     Balloons  without  men  have 

risen   eighteen  miles.     At  this 


Y^igh  Clouds  (lOmiles) 
tow  Cloudsfysmile ) 


_  Fig.  19.     Diagram  to  show  relative 
altitudes  in  the  atmosphere. 


height  the  air  is  still  dense 
enough  to  carry  the  balloon. 
This  shows  that  the  air  extends 
up  more  than  eighteen  miles. 

(3)  On  almost  any  clear 
night  "shooting  stars"  may  be 
seen.  Shooting  stars,  or  me- 
teors, are  small,  solid  bodies 
which  come  into  the  earth's 
atmosphere  from  space  outside. 
They  are  very  cold  when  they 
enter  the  atmosphere,  for  the  temperature  of  space  is  very  low 
(probably  about  — 4S9°F.)-  In  passing  through  the  atmosphere, 
meteors  are  heated  by  friction  with  the  air,  and  when  they  get  red-hot, 
they  may  be  seen.  The  height  at  which  they  begin  to  glow  has  been 
calculated  in  some  cases,  and  found  to  be,  at  a  maximum,  nearly  200 
miles  above  sea-level  This  shows  that  the  atmosphere  is  much  more 
than  200  miles  high,  for  the  meteors  micst  have  come  through  the  rare, 
cold,  upper  air  a  long  distance  before  becoming  red-hot  by  friction  with  it. 
From  these  considerations  it  appears  to  be  certain  that  the  air 
extends  more  than  200  miles  above  the  rest  of  the  earth,  but  how 
much  more  is  unknown.  Except  for  a  few  miles  near  its  bottom,  it 
is,  of  course,  very  thin  (rare). 


Composition 

Principal  constituents.  The  composition  of  the  atmosphere  is 
nearly  the  same  at  all  times  and  at  all  places  where  it  has  been  ana- 
lyzed. In  its  lower  parts,  at  least,  it  is  made  up  chiefly  of  two  gases 
—  (i)  nitrogen,  which  makes  up  about  78  per  cent  of  dry  air,  and  (2) 


IMPURITIES   IN   THE   AIR  29 

oxygen,  which  makes  nearly  21  per  cent.  Some  scientists  think  its 
composition  at  great  heights  may  be  very  different  from  that  below. 

Besides  these  two  gases,  there  are  several  lesser  constituents,  two 
of  which,  carbon  dioxide  and  water  vapor,  are  very  important.  The 
former  makes  up  about  Vioooo  by  weight  of  the  whole  atmosphere, 
and  its  amount  is  nearly  constant  from  day  to  day,  and  from  year  to 
year.  Water  vapor  is  water  in  particles  too  small  to  be  seen.  The 
total  amount  in  the  atmosphere  is  not  known  to  vary  much,  but  the 
amount  varies  greatly  from  place  to  place,  and  it  varies  much  from 
time  to  time  in  the  same  place.  Even  in  the  driest  deserts  the  air  is 
never  without  water  vapor.  Several  other  gases  exist  in  the  air,  but 
among  them  ozone  only  is  known  to  be  of  much  importance. 

The  gases  of  the  air  are  mixed  with  one  another,  and  each  of  them 
retains  its  own  qualities  in  the  mixture.  Oxygen  behaves  much  as  if 
no  nitrogen  were  present,  and  the  nitrogen  as  if  there  were  no  oxygen. 

Impurities.  The  air  always  contains  some  gases  which  are 
impurities,  though  they  are  not  necessarily  harmful  to  life.  Some 
such  gases  arise  from  the  burning  and  decay  of  organic  matter, 
others  from  chemical  processes  used  in  manufacturing,  and  still  others 
from  volcanic  and  other  vents  in  the  earth's  crust.  Although  the 
total  amount  of  gas  which  enters  the  air  in  these  ways  is  small  in 
comparison  with  the  volume  of  the  atmosphere,  it  would  seem  very 
great  if  stated  in  terms  of  weight  or  volume.  For  example,  it  is 
estimated  that  at  least  1,000,000,000  cubic  feet  of  natural  gas  escape 
unused  into  the  air  each  day  in  the  United  States.  Quantities  of  gas 
are  poured  into  the  air,  too,  from  chimneys.  The  air  always  contains, 
as  impurities,  numerous  solid  particles,  such  as  dust,  and  germs  or 
other  organic  matter.  These  vary  in  amount  and  character  from 
place  to  place,  and  from  time  to  time. 

Relations  of  the  Different  Constituents  to  Life 

Nitrogen.  Nitrogen  is  inactive.  Though  it  enters  the  lungs 
with  oxygen  in  breathing,  it  does  not  appear  to  be  of  direct  use  to 
animals.  Indeed,  its  chief  function  in  relation  to  life  is  often  said 
to  be  "to  dilute  the  oxygen."  It  is  important  to  note,  however, 
that  indirectly  nitrogen  is  of  great  importance  to  both  plant  and 
animal  life.  Most  plants  use  the  small  quantities  of  nitrogen  com- 
pounds in  the  soil.  Nearly  all  crops,  if  grown  year  after  year  in  the 
same  place,  take  out  so  much  of  the  nitrogenous  matter  as  to  decrease 


so    NATURE  AND  FUNCTIONS  OF  THE  ATMOSPHERE 

the  fertility  of  the  soil.  A  few  plants,  such  as  clover,  alfalfa,  peaS; 
and  beans,  add  nitrogen  to  the  soil.  Certain  bacteria  associated 
with  these  plants  take  nitrogen  from  the  air  and  combine  it  with  other 
elements,  and  the  plants  then  store  it  in  their  roots,  stalks,  etc.  It 
is  therefore  important  to  grow  nitrogen-fixing  plants  in  rotation  with 
other  crops,  and  turn  them  under  the  soil.' 

Oxygen.  Oxygen  from  the  air  is  consumed  all  the  time  by  ani- 
mals. Air-breathing  animals  take  it  from  the  air  directly,  and  water- 
breathing  animals  take  it  from  the  water  in  which  it  is  dissolved. 
Oxygen  is  used  by  plants  also,  especially  by  green  plants,  and  it  is 
used  wherever  combustion  (burning)  or  decay  is  going  on,  for  com- 
bustion is  primarily  the  union  of  oxygen  with  carbon,  and  decay 
is  very  slow  combustion.  The  heat  developed  by  combustion  (as 
of  coal)  warms  houses,  and  produces  steam  to  run  trains,  drive 
machinery,  and  serve  man  in  many  other  ways.  Oxygen  from 
the  air  combines  with  various  constituents  of  rocks  to  form  new  com- 
pounds, and  in  so  doing  helps  to  form  soil  (p.  162). 

In  spite  of  the  fact  that  oxygen  is  being  consumed  all  the  time, 
its  amount  does  not  appear  to  grow  less  from  year  to  year.  It  must, 
therefore,  be  supplied  to  the  air  about  as  fast  as  it  is  used  up.  Plants 
break  up  the  carbon  dioxide  of  the  air  into  carbon  and  oxygen,  and 
set  some  of  the  oxygen  free.  This  is  the  greatest  source  of  supply. 
Small  amounts  of  oxygen  also  reach  the  atmosphere  from  volcanic 
vents,  and  in  other  ways.  It  will  be  seen  that  plants,  through  their 
relation  to  oxygen  and  nitrogen,  play  an  important  part  in  supplying 
animals  with  both  these  elements. 

Carbon  dioxide.  The  carbon  dioxide  of  the  air,  though  a  small 
constituent,  is  extremely  important.  It  is  being  made  constantly 
by  the  burning  of  all  kinds  of  fuel  and  by  the  decay  of  all  organic 
matter.  It  is  also  added  to  the  air  by  the  breathing  of  animals. 
Every  1,000,000  human  beings  breathe  out  about  2.5  tons  per  hour. 
It  also  comes  out  of  many  volcanic  vents  in  great  quantities. 

From  these  various  sources,  carbon  dioxide  is  supplied  to  the  atmosphere 
rapidly.  About  three-fourths  of  common  soft  coal  is  carbon.  The  carbon  of  a  ton 
of  such  coal,  united  with  oxygen  from  the  air  (slbs.  of  carbon  unite  with  Slhs.  of 
oxygen),  would  make  more  than  2^4  tons  of  carbon  dioxide,  all  of  which  goes  into 
the  atmosphere.  A  ton  of  hard  coal,  which  contains  more  carbon,  would  produce 
still  more  carbon  dioxide.  Nearly  a  billion  tons  of  coal  are  mined  each  year,  and 
most  of  this  is  burned.  WTien  all  sources  of  carbon  dioxide  are  considered,  it  seems 
safe  to  say  that  carbon  dioxide  is  being  supplied  to  the  atmosphere  at  the  rate  of 
about  75  tons  per  second. 


CARBON  DIOXIDE  AND   LIFE  31 

Because  of  its  close  relations  to  combustion,  respiration,  and 
decay,  the  amount  of  carbon  dioxide  in  the  air  of  cities  is  greater  than 
in  the  open  country.  The  amount  in  the  air  of  London  occasionally 
becomes  five  times  the  normal  quantity,  while  in  badly  ventilated 
schoolrooms,  theaters,  and  workshops,  it  is  sometimes  ten  times  the 
normal  amount.  The  conditions  which  increase  the  amounts  of 
carbon  dioxide  in  city  air  usually  increase  the  amounts  of  various 
other  harmful  gases.  Such  conditions  are  injurious  to  health.  The 
widespread  movement  to  "purify  city  air,"  largely  by  doing  away 
with  smoke,  is  an  attempt  to  remedy  these  conditions. 

In  spite  of  constant  additions,  the  amount  of  carbon  dioxide  in 
the  air  does  not  increase  permanently  enough  to  be  noted.  This  gas, 
therefore,  must  be  taken  out  of  the  atmosphere  about  as  rapidly  as 
it  comes  in.  It  is  taken  from  the  air  chiefly  (i)  by  green  plants,  of 
which  it  is  the  main  food,  and  (2)  by  uniting  with  mineral  matter 
in  the  solid  part  of  the  earth.  It  supports  not  only  most  plants,  but 
indirectly  most  animals,  for  the  latter  feed  on  vegetation,  or  on 
other  animals  that  live  on  plants.  By  uniting  with  mineral  matter 
it  helps  to  form  soil. 

The  carbon  dioxide  of  the  air  has  still  other  important  functions. 
The  earth  is  radiating  heat  into  space  all  the  time,  somewhat  as  a  hot 
stove  radiates  heat  into  its  surroundings,  and  carbon  dioxide  has  the 
power  of  holding  much  of  this  heat.  It  therefore  serves  as  a  blanket 
to  hold  in  the  heat  of  the  earth,  and,  thin  as  the  blanket  is,  it  is  more 
effective,  in  this  respect,  than  the  denser  blanket  of  oxygen  and 
nitrogen.  If  it  were  thicker,  the  temperature  would  be  still  higher. 
It  is  thought  possible  that  at  certain  times  in  the  distant  past,  as 
when  magnolias  grew  in  Greenland,  the  amount  of  carbon  dioxide  in 
the  air  may  have  been  greater  than  now;  and  that  at  other  times, 
when  the  climate  was  cold  in  low  latitudes,  the  amount  may  have  been 
much  less  than  now. 

Water  vapor.  The  water  vapor  in  the  atmosphere  is  a  variable 
quantity.  It  is  all  the  time  entering  the  atmosphere  by  evaporation, 
and  it  is  all  the  time  being  condensed  and  precipitated  from  the 
atmosphere  as  rain,  snow,  etc.,  to  be  again  evaporated,  condensed, 
and  precipitated.  The  larger  part  of  both  water  vapor  and  carbon 
dioxide  is  in  the  lower  part  of  the  atmosphere.  Like  much  of  the 
carbon  dioxide,  the  water  vapor  is  making  continuous  rounds.  Its 
precipitation  supplies  the  water  for  wells,  the  flow  of  springs,  the 
maintenance  of  lakes,  streams,  and  glaciers,  and  for  the  life  of  plants 


32    NATURE  AND  FUNCTIONS  OF  THE  ATMOSPHERE 

and  animals.  The  bodies  of  animals,  including  human  beings,  are 
about  four-fifths  water.  The  tissues  of  annual  plants  are  three- 
fourths  water;  of  perennials,  nearly  half.  To  produce  a  bushel  of 
corn,  from  lo  to  20  tons  of  water  are  required. 

The  amount  of  water  vapor  which  the  atmosphere  is  capable  of 
containing  at  any  time  depends  on  temperature;  but  other  things, 
such  as  the  available  supply,  help  to  determine  the  amount  which 
there  is  in  the  air  in  any  one  place.  Like  the  carbon  dioxide,  the 
water  vapor  of  the  air  helps  to  keep  the  earth  warm. 

Dust.  All  solid  particles  held  in  the  air  are  dust.  They  are 
not  ordinarily  seen  except  on  dry,  windy  days,  but  dust  from  the  air 
is  constantly  settling  everywhere,  indoors  and  out,  whenever  the 
air  is  dry.  Dust  may  be  seen  readily  indoors  if  a  room  is  darkened 
and  light  allowed  to  enter  through  a  narrow  crack  or  small  hole. 
Even  air  which  appears  clear  may  in  this  way  be  seen  to  contain 
countless  particles  of  solid  matter.  The  amount  of  dust  is  sometimes 
very  great,  as  over  cities  and  in- dry  and  windy  regions.  During  the 
fogs  of  February,  1891,  it  was  estimated  that  the  amount  of  dust 
deposited  on  roofs  in  and  near  London  was  six  tons  per  square  mile. 
Dust-polluted  air  is  believed  to  favor  diseases  of  the  lungs,  like 
tuberculosis. 

Some  years  ago  a  method  was  devised  for  counting  the  dust  particles  in  a 
given  volume  of  air.  The  result  showed  that  in  the  air  of  great  cities  there  are 
hundreds  of  thousands  of  dust  particles  in  each  cubic  centimeter  of  air  (a  cubic 
centimeter  is  less  than  '/16  of  a  cubic  inch);  and  that  even  in  the  pure  air  of  the 
country,  far  from  towns  and  factories,  there  are  hundreds  of  motes  per  cubic  centi- 
meter. 

Like  carbon  dioxide  and  water  vapor,  most  of  the  dust  is  found  be- 
low an  altitude  of  10,000  feet.  Its  relative  absence  at  high  altitudes 
increases  the  intensity  of  the  sunshine  there  by  day,  and  helps  to 
bring  about  low  temperatures  at  night. 

Dust  particles  in  the  atmosphere  are  important  in  several  other 
ways.  They  scatter  the  light  of  the  sun  in  such  a  way  as  to  illuminate 
the  whole  atmosphere.  Without  dust  in  the  air,  all  shady  places  would 
be  in  darkness.  The  sun  would  appear,  probably  in  dazzling  brilliance, 
shining  from  a  black  sky  in  which  the  stars  would  be  visible  even  in 
the  daytime.  The  blue  color  of  the  sky  and  the  sunset  and  sunrise 
tints  are  influenced  by  the  dust  in  the  atmosphere.  Dust  particles 
also  serve  as  centers  about  which  water  vapor  condenses- 


QUESTIONS  33 


Questions 

1.  State  the  conditions  (all  of  them)  which  would  tend  to  make  the  country 
air  dusty  at  a  given  point  in  northern  United  States. 

2.  What  conditions  favor  an  increase  in  the  amount  of  dust  in  the  air  of  cities 
in  summer?     In  winter? 

3.  Compare  and  contrast  the  purity  of  the  air  (i)  over  oceans  and  over 
lands;   (2)  in  dry  and  in  moist  regions;  and  (3)  at  high  and  at  low  altitudes. 

4.  Would  you  expect  the  average  amount  of  carbon  dioxide  to  be  greater  in 
the  air  of  cities  or  of  the  open  country?  Why?  What  processes  tend  to  equalize 
the  amount  over  country  and  cities? 

5.  Give  at  least  three  reasons  why  the  amount  of  carbon  dioxide  in  the  air 
(especially  of  great  cities)  tends  to  vary  in  amount  between  summer  and  winter. 

6.  Why  do  people  accustomed  to  low  altitudes  breathe  very  much  faster  in 
high  altitudes? 

7.  Indicate  various  ways  in  which  the  extreme  elasticity  of  the  air  favors 
human  activities. 


CHAPTER  V 
CLIMATIC   FACTORS:  TEMPERATURE 

General  Considerations 

Besides  the  composition  of  the  atmosphere,  various  other  things 
connected  with  it  are  of  great  importance  to  life.  The  things  which 
make  up  climate  {climatic  factors)  are  especially  important.  The 
chief  climatic  factors  are  (i)  temperature,  (2)  moisture,  and  (3)  air 
movements,  or  wind. 

Importance  of  heat.  Were  it  not  for  the  effect  of  the  atmosphere 
on  temperature,  life  could  not  endure  the  heat  of  day  or  the  cold  of 
night,  and  the  earth  would  be  a  desolate,  lifeless  waste.  The  tem- 
perature which  most  concerns  land  life  is  the  temperature  of  the  air 
in  which  it  lives.  The  air  is  warmed  chiefly  by  the  sun.  The  heat- 
ing power  of  the  sun  is  proved  by  the  fact  that  days  are  warmer  than 
nights,  and  that  sunny  days  are  warmer  than  cloudy  ones.  The 
rare  exceptions  to  these  general  facts  need  not  be  considered  now. 

Measurement  of  heat.  Variations  of  temperature  from  time  to  time  and 
from  place  to  place  are  so  important  that  it  is  necessary  to  have  some  easy  way  of 
measuring  and  recording  them.  Temperature  is  measured  by  the  thermometer, 
which  consists  of  a  glass  tube  of  uniform  diameter,  except  for  a  bulb  at  the  lov/er 
end.  The  bulb  and  the  lower  part  of  the  tube  are  filled  with  some  Hquid,  generally 
mercury,  and  this  is  heated  until  it  boils.  The  boihng  mercury  fills  the  tube  and 
expels  all  air,  and  while  it  is  boihng  the  tube  is  sealed,  the  heat  being  withdrawn  at 
the  same  moment.  On  cooling,  the  mercury  contracts  and  fills  the  lower  part  of 
the  tube  only.  Whenever  the  temperature  rises,  the  mercury  expands  and  rises 
in  the  tube,  and  when  the  temperature  falls,  the  mercury  contracts  and  sinks.  The 
amount  of  rise  or  fall  of  the  mercury  shows  the  amount  of  change  of  temperature. 
A  scale  is  marked  on  the  tube  so  that  the  temperature  may  be  read  from  it. 
Two  scales  are  in  common  use  —  the  Fahrenheit  (F.)  and  the  Centigrade  (C.)-  On 
the  Fahrenheit  scale  the  temperature  of  boiling  water  (at  sea-level  under  normal 
pressure)  is  marked  212°;  on  the  Centigrade  scale,  100°  (Fig.  20).  The  tempera- 
ture of  melting  ice  (freezing  point)  is  marked  32°  on  the  former  scale,  and  0°  (zero) 
on  the  latter.  Between  the  freezing  and  the  boiling  point  on  the  Fahrenheit  scale 
there  are  180  degrees,  and  on  the  Centigrade  scale  100  degrees.  It  follows  that 
1°  C.  is  equal  to  14/5°  F.  Zero  on  the  Fahrenheit  scale  is  32°  below  the  freezing 
point,  and  20°  below  zero  Fahrenheit  (written  —  20°  F.)  means  52°  (32°-!- 20°) 

34 


HEAT  FROM   THE   SUN 


35 


below  the  freezing  point.     The  Centigrade  scale  is  simpler  than  the  Fahrenheit, 
and  is  used  generally  in  scientific  work  and  in  most  European  countries. 

We  often  have  occasion  to  use  the  temperature  of  a  given  place  at  a  given  time, 
as  that  of  New  York  at  noon  on  July  4th;  but  we  also  have  occasion  to  use  the 
records  of  temperature  in  other  ways.  From  a  sufficient  number  of  temperature 
records,  spread  properly  over  a  year,  an  average  temperature  for  that  year  may  be 
obtained.  Similarly,  averages  for  shorter  periods,  as  seasons,  months,  and  days, 
are  possible,  called  average  seasonal,  monthly,  and  daily 
temperatures.  The  average  temperature  of  one  year  tor  a 
given  place  is,  as  a  rule,  somewhat  different  from  that  of 
the  preceding  or  following  year.  The  average  temperature 
for  a  goodly  number  of  years  gives  its  mean  annual  tem- 
perature. Similarly,  it  is  necessary  to  take  the  averages 
for  many  Januarys  to  get  the  mean  monthly  temperature 
for  that  month.  The  highest  temperature  during  any 
period  is  its  maximum  temperature  and  the  lowest,  its 
minimum  temperature. 


lorf- 


60- 


20- 


to-- 


o-^ 


-211* 


-140* 


-6V 


-50' 


-32* 


-<T.7'~|-  O- 


Fig.  20.  Diagram 
to  represent  Fahren- 
heit and  Centigrade 
scales. 


Sun  heating :  insolation.  The  northern  and 
southern  hemispheres  receive  the  same  amount 
of  heat  from  the  sun  each  year,  but,  because  of 
the  inclination  of  the  earth's  axis,  they  do  not 
receive  the  same  amounts  at  the  same  seasons. 
Both  receive  the  same  amounts  of  heat  per  day 
only  at  the  times  of  equinox.  The  amount  of 
heat  received  by  the  surface  of  land  and  water  is 
far  less  than  the  amount  coming  to  the  top  of 
the  atmosphere,  for  much  is  absorbed  in  passing 
through  the  air. 

(i)  Other  things  being  equal,  any  part  of 
the  earth  should  get  most  heat  per  day  when 
the  sun  shines  there  the  greatest  number  of  hours.  During  a  part 
of  the  summer  of  the  northern  hemisphere,  latitudes  above  66>^° 
have  sunshine  continuously  (except  for  clouds)  for  more  than  24 
hours.  So  far  as  hours  of  sunshine  are  concerned,  therefore, 
these  latitudes  should  then  receive  more  heat  per  day  than  other 
parts  of  the  earth.  If  there  were  no  atmosphere,  the  surface  of 
the  earth  at  the  North  Pole  would  receive,  on  the  21st  of  June, 
about  one-third  more  heat  during  24  hours  than  the  surface  of  an 
equal  area  at  the  equator.  But  the  amount  of  heat  which  reaches 
the  bottom  of  the  air  at  the  pole  on  the  21st  of  June  is  much 
less  than  that  received  at  the  bottom  of  the  atmosphere  at  the 
equator. 


36 


CLIMATIC   FACTORS:    TEMPERATURE 


(2)  Other  things  being  equal,  the  surface  of  the  land  or  water  gets 
most  heat  where  the  sun's  rays  are  most  nearly  vertical,  because  (a) 
the  rays  are  there  most  concentrated,  and  (b)  they  pass  through 
a  less  thickness  of  the  air.  This  is  shown  by  Fig.  21.  A  given 
bundle  of  rays,  i,  falling  vertically  on  the  surface,  is  distributed 

over  a  given  area,  while  an 
equal  bundle  of  rays,  2,  falling 
obliquely  on  the  surface,  is 
spread  over  a  greater  area,  and 
therefore  heats  each  part  less. 
The  rays  oblique  to  the  sur- 
face, 2,  have  passed  through  a 
greater  thickness  of  air,  and 
more  of  their  heat  has  been  ab- 
sorbed by  it  before  they  reach 
the  surface  of  the  land  or  water. 
These  facts  help  to  explain  why 
the  surface  at  the  poles  does  not 
get  warmer  than  an  equal  area 
at  the  equator,  even  with 
months  of  continuous  sunshine 
at  the  former  places,  and  but 
12  hours  at  a  time  at  the  latter. 
The  snow  and  ice  of  polar  regions  prevent  them  from  getting  warm, 
even  during  the  months  when  much  heat  is  received  (p.  37). 

The  angle  at  which  the  sun 's  rays  reach  the  earth  varies  from  place 
to  place,  and  from  time  to  time  at  the  same  place,  because  of  the 
inclination  of  the  earth's  axis.  This  is  illustrated  by  Figs.  8  and  9, 
which  have  been  explained. 

Distribution  of  insolation.  From  Fig.  10,  which  has  been 
studied,  we  see  that  when  the  sun's  rays  come  to  th«  earth  from  the 
direction  W  (perpendicular  23^^°  south  of  the  equator),  they  are 
more  oblique  than  at  any  other  time  in  the  northern  hemisphere,  and 
less  oblique  than  at  any  other  time  in  the  southern  hemisphere.  At 
the  same  time  the  days  are  longer  in  the  southern  hemisphere  than  in 
the  northern.  Hence  there  are  two  reasons  why  the  southern  hemi- 
sphere receives  more  heat  than  the  northern  at  this  season,  namely  (i) 
more  nearly  vertical  rays,  and  (2)  more  hours  of  sunshine. 

After  the  time  (winter  solstice,  December  22d)  when  the  sun's 
rays  are  vertical  at  23^^°  S.,  they  become  perpendicular  to  the  sur- 


Fig.  21.  Diagram  to  illustrate  the 
unequal  heating  at  the  bottom  of  the 
atmosphere,  due  to  the  angle  at  which 
the  rays  of  the  sun  reach  the  surface  of 
the  earth.  The  dotted  line  may  be  taken 
to  represent  the  outer  limit  of  the  atmos- 
phere. 


DISTRIBUTION  OF   SUN'S   HEAT  37 

face  in  latitudes  farther  and  farther  north,  and  on  March  21st  they 
are  vertical  at  the  equator.  Days  and  nights  are  then  equal  every- 
where, because  all  parallels  are  cut  into  two  equal  parts  by  the 
circle  of  illumination  (p.  12),  and  the  sun's  rays  are  equally 
oblique  in  corresponding  latitudes  north  and  south  of  the  equator. 
Any  latitude  in  one  hemisphere  is  then  receiving  the  same  am.ount 
of  heat  as  the  corresponding  latitude  in  the  other  hemisphere. 
This  condition  would  be  permanent  if  the  axis  of  the  earth  were  not 
inclined. 

After  March  21st,  the  sun  continues  its  apparent  journey  north- 
ward until  June  21st,  when  its  rays  are  vertical  at  the  tropic  of 
Cancer,  23^°  N.  The  days  of  the  northern  hemisphere  are  then 
longest  and  the  nights  shortest,  and  the  rays  of  the  sun  are  less 
oblique  in  this  hemisphere  than  at  any  other  time.  At  this  time, 
therefore,  the  northern  hemisphere  is  being  heated  more  than  at  any 
other. 

From  June  21st  to  December  2  2d,  the  sun  appears  to  move  so  that 
its  rays  become  vertical  farther  and  farther  south,  and  the  preceding 
changes  are  reversed. 

The  latitudes  where  the  sun's  rays  fall  vertically  range  from  the 
tropic  of  Cancer  to  the  tropic  of  Capricorn;  and  the  sun's  rays  are,  on 
the  average,  least  oblique  between  these  limits.  This  is  why  low 
latitudes  are,  on  the  whole,  warmer  than  high  latitudes. 

The  density  of  the  atmosphere  also  affects  the  amount  and  in- 
tensity of  the  insolation  received  by  the  surface  of  the  earth.  On 
mountains  the  less  density  of  the  air  means  more  intense  sunlight, 
and  a  greater  amount  of  heat  per  unit  of  land  surface,  than  is  received 
at  sea-level  (p.  39).  One  effect  of  this  is  seen  in  the  rapid  growth  of 
plants  on  mountains  in  early  summer. 

Distribution  of  temperature.  The  temperature  of  one  place  is 
not  necessarily  higher  than  that  of  another  because  it  receives  more 
heat.  The  region  about  the  North  Pole  does  not  get  very  warm, 
even  when  it  receives  much  heat,  because  much  of  the  heat  received 
is  used  in  melting  ice  and  in  warming  ice-cold  water,  which  is  warmed 
very  slowly,  and  flows  away  as  soon  as  the  heating  is  well  begun. 
Mountain  tops  are  also  generally  cold  in  spite  of  the  intensity  of  inso- 
lation there. 

After  the  heat  from  the  sun  has  been  received  by  the  earth,  it  is 
re-distributed  to  some  extent,  with  the  general  result  that  the  parts 
which  get  more  by  insolation  share  their  heat  with  the  parts  which 


38  CLIMATIC   FACTORS:    TEMPERATURE 

get  less.  The  distribution  of  actual  temperature,  therefore,  differs 
much  from  the  simple  distribution  which  insolation  would  give. 

There  are  three  ways  in  which  the  air  receives,  loses,  and  transfers 
heat.     These  are  radiation,  conduction,  and  convection. 

(i)  Radiation.  The  sun  always  radiates  heat,  and  the  surface 
which  its  rays  strike  is  warmed  by  absorption  of  the  radiated  heat. 
A  body  need  not  be  glowing  hot,  like  the  sun,  or  like  fire,  to  radiate 
heat.  The  radiators  in  our  houses  radiate  heat  when  they  contain 
hot  water  or  steam.  The  body  which  radiates  heat  is  itself  cooled. 
Thus  hot  iron  soon  cools  in  the  air,  because  it  radiates  its  heat.  The 
land  warmed  by  the  absorption  of  heat  radiated  from  the  sun  during 
the  day  is  cooled  by  the  radiation  of  its  heat  at  night.  The  absorp- 
tion of  heat  by  day  and  its  loss  by  night  give  variations  of  temperature 
between  day  and  night.  If  the  day  is  long  and  the  night  short,  ab- 
sorption of  heat  from  the  sun  by  day  exceeds  radiation  by  night,  and 
the  land  tends  to  become  warmer,  as  in  spring  and  early  summer. 
If  the  day  is  short  and  the  night  long,  radiation  of  heat  will  be  greater 
than  absorption,  and  the  land  will  become  colder,  as  in  autumn  and 
early  winter. 

(2)  Conduction.  If  one  end  of  an  iron  poker  is  put  in  the  fire,  the 
other  end  becomes  hot.  The  heat  passes  from  one  end  to  the  other. 
This  method  of  passing  heat  along  is  condtiction.  Any  cold  body 
in  contact  with  a  hot  body  is  warmed  by  conduction.  The  hand 
is  warmed  by  conduction  when  placed  on  anything  which  feels  warm ; 
it  is  cooled  by  conduction  when  placed  on  something  which  feels  cool. 
The  bottom  of  the  air  is  warmed  by  contact  with  the  land  (that  is,  by 
conduction)  wherever  the  temperature  of  the  land  is  higher  than  that 
of  the  air.  Conduction  from  the  land  to  the  bottom  air  has  an  im- 
portant effect  on  the  temperature  of  the  air  just  above  the  ground. 

(3)  Convection.  When  a  kettle  of  water  is  placed  on  a  hot  stove, 
the  water  in  the  bottom  is  heated  by  conduction,  that  is,  by  contact 
with  the  hot  kettle.  The  heating  of  the  water  causes  it  to  expand, 
and  when  the  water  in  the  bottom  of  the  kettle  expands,  it  becomes 
lighter  than  the  water  above.  The  heavier  water  above  sinks  and 
pushes  the  lighter  water  below  up  to  the  top.  This  movement  is 
convection.  Another  illustration  of  convection  is  afforded  by  stoves, 
fireplaces,  and  furnaces.  A  thin  sheet  of  light  paper  may  be  held  up 
for  a  moment  by  the  rising  air  over  a  hot  stove,  or  even  carried  up 
if  the  convection  current  is  strong  enough.  Again,  as  the  air  in  a 
chimney  is  heated,  it  expands  and  becomes  less  dense  than  the  air 


CONVECTION   CURRENTS 


39 


Fig.  2  2.  The  first  rise  of  air,  as  a 
result  of  heating,  is  due  to  the  expansion 
of  the  part  heated. 


Fig.  23.  The  permanent  heating  of 
the  air  over  a  region  gives  rise  to  per- 
manent convection  currents. 


about  it.  The  cooler,  denser  air  about  the  base  of  the  chimney  or 
stove  crowds  in  below  the  expanded  air  in  the  chimney,  and  pushes 
it  up  out  of  the  chimney.  Since  the  air  entering  the  chimney  from 
below  is  being  heated  and  expanded  all  the  time,  the  up-draught  con- 
tinues as  long  as  there  is  fire. 
Every  draught  from  a  chimney 
is  an  example  of  convection. 

When  the  surface  of  the  land 
is  warmed  by  the  absorption  of 
heat  from  the  sun,  it  warms  the 
air  above  both  by  conduction 
and  by  radiation.  The  lands 
of  low  latitudes  are  heated  more 
than  others.  The  heated  air 
over  the  heated  land  expands. 
If  the  air  in  a  given  region 
were  expanded  as  shown  in  Fig. 
22,  the  air  at  the  top  of  the 
expanded  column  would  flow 
away,  much  as  water  would  un- 
der similar  conditions.  After  this  takes  place,  the  amount  of  air  at 
the  base  of  the  column  h  will  be  less  than  the  amount  at  the  same  level 
outside  the  heated  area,  and  air  from  outside  the  heated  column  will 
flow  in.  This  inflow  will  push  up  the  column  of  expanded  air,  and 
further  overflow  above  will  cause  further  inflow  below.  If  the  heat- 
ing continues,  a  permanent  convection  current  is  established  in  the 
heated  area  (Fig.  23).  Such  movements  of  air  are  important  not  only 
in  distributing  temperature,  but  also  in  causing  winds,  clouds,  and 
storms. 

The  atmosphere  is  heated  (i)  by  the  absorption  of  the  sun's  rays 
as  they  come  through  it,  (2)  by  the  absorption  of  heat  radiated  from 
land  and  water,  and  (3)  by  conduction  from  warm  land  or  water  to 
the  lower  air.  The  amount  of  heat  absorbed  by  air  from  the  direct 
rays  of  the  sun  depends  on  the  distance  the  rays  travel  in  it,  that  is, 
on  the  obliquity  of  the  sun's  rays  (Fig.  21).  When  the  sun  is  vertical 
at  the  equator,  its  rays  pass  through  about  twice  as  much  atmosphere 
in  latitude  60°,  and  about  ten  times  as  much  in  latitude  85°,  as  they 
do  in  latitude  0°.  The  amount  of  absorption  of  sun-heat  by  the  air, 
therefore,  varies  with  latitude.  About  half  of  it  is  absorbed  by  the 
air  at  the  equator,  and  about  four-fifths  at  the  poles,  as  compared 


40  CLIMATIC  FACTORS:    TEMPERATURE 

with  the  total  amount  which  would  reach  the  earth  in  those  latitudes 
if  there  were  no  atmosphere.  In  general,  the  amount  of  heat  absorbed 
by  the  atmosphere  is  more  than  50  per  cent  of  the  total  amount 
coming  to  the  earth  from  the  sun. 

The  heat  radiated  into  the  air  from  below  is  absorbed  by  the  air 
much  more  readily  than  that  coming  from  the  sun  directly.  The 
lower  air  consequently  is  heated  by  radiation  from  below  more  than  by 
direct  insolation. 

After  heat  is  received  from  the  sun,  therefore,  it  is  re-distributed 
by  radiation,  conduction,  and  convection.  Movements  of  air  (winds) 
and  movements  of  water  (especially  ocean  currents)  also  distribute 
heat.  Without  t  lese  movements  of  air  and  water,  the  average  tem- 
perature of  the  equator  would  be  much  higher  than  now,  and  that  of 
the  poles  much  loM^er.  These  changes  would  be  destructive  to  many 
forms  of  life. 

Temperature  of  land  and  water.  Land  is  heated  by  insolation 
four  or  five  times  as  fast  as  water,  for  several  reasons: 

(i)  A  given  amount  of  heat  raises  the  temperature  of  soil  and 
rock  more  than  that  of  water. 

(2)  Water  is  a  good  reflector,  while  land  is  not;  the  latter,  there- 
fore, absorbs  a  larger  proportion  of  the  heat  of  the  sun 's  rays. 

The  amount  of  heat  reflected  from  a  water  surface  increases  with  increasing 
obliqueness  of  the  sun's  rays.  At  the  equator,  40  per  cent  of  the  insolation  goes 
into  heating  the  water;  in  latitude  60^,  less  than  5  per  cent.  A  familiar  result  of 
the  reflection  of  heat  from  water  appears  in  the  intensity  of  sun-burn  received  on 
water.     Snow-covered  land  and  bare  white  sand  reflect  heat  much  as  water  does. 

(3)  Land  radiates  heat  more  readily  than  water  does. 

(4)  Convection  movements  take  place  in  water  as  soon  as  its 
surface  is  heated.  This  prevents  excessive  heating  at  any  one  point. 
The  land,  on  the  other  hand,  is  without  movements  of  convection. 

(5)  There  is  more  evaporation  from  a  water  surface  than  from 
land,  other  conditions  being  the  same,  and  evaporation  cools  the 
surface  from  which  it  takes  place.  A  wet  soil,  receiving  the  same 
amount  of  the  sun's  rays,  remains  cooler  than  a  dry  soil.  The  hot 
sand  of  the  desert  is  an  example  of  this  effect  on  the  warming  of  the 
land. 

(6)  Light  and  heat  penetrate  water,  but  not  soil  and  rock  to 
any  great  extent.  The  heat  of  insolation  is  therefore  distributed 
through  a  greater  thickness  of  water  than  of  soil.  Being  confined  to 
the  surface  of  the  soil,  the  temperature  of  the  latter  is  made  higher. 


CONTRASTS  OF  SEASONS  41 

Since  the  temperature  of  air  tends  to  be  the  same  as  that  of  the 
surface  on  which  it  lies,  the  presence  of  land  or  water  is  an  important 
factor  in  determining  the  temperature  of  the  air  above. 


Seasons 
In  Middle  Latitudes 
In   middle   latitudes,    the   seasons   are 'four  —  spring,    summer, 
autumn,  and  winter.     Each  season  has  characteristics  of  its  own, 
but  each  grades  into  the  one  which  follows. 

In  the  United  States,  March,  April,  and  May  are  commonly  called  the  spring 
months;  June,  July,  and  August  the  summer  months;  September,  October,  and 
November  the  autumn  months;  and  December,  January,  and  February  the  winter 
months.  In  the  southern  hemisphere,  spring  comes  in  September,  October,  and 
November;  summer  in  December,  January,  and  February,  and  so  on.  The 
vernal  equinox  of  the  northern  hemisphere  is  the  autumnal  equinox  of  the  southern, 
and  the  summer  solstice  of  the  northern  is  the  winter  solstice  of  the  southern.  The 
definition  of  the  seasons  given  above  is  based  on  temperature,  the  warmest  three 
months  being  summer,  and  the  coldest  three,  winter.  The  seasons  are  sometimes 
defined  in  a  different  way.  Thus  spring  is  sometimes  regarded  as  the  time  between 
the  vernal  equinox  and  the  summer  solstice;  summer  the  time  from  the  summer 
solstice  to  the  autumnal  equinox,  and  so  on. 

Summer  and  winter  temperatures.  The  summer  heat  of  middle 
latitudes  is  due  (i)  to  the  high  altitude  of  the  midday  sun  above  the 
horizon,  giving  less  oblique  rays  with  a  shorter  path  through  the 
atmosphere,  and  (2)  to  the  long  days  and  short  nights.  More  heat 
is  received  during  the  long  day  than  is  lost  during  the  short  night. 
The  reverse  of  these  conditions  accounts  for  the  cold  of  winter,  though 
during  the  winter  of  the  northern  hemisphere  the  earth  is  3,000,000 
miles  nearer  the  sun  than  in  summer. 

.A  consideration  of  Figs.  3  and  9  will  make  it  clear  why  the  seasons  are  reversed 
in  the  two  hemispheres.  One  result  of  this  difference  of  seasons  in  opposite  hemi- 
spheres at  the  same  time  is  that  crops  in  the  middle  latitudes  of  the  southern  hemi- 
sphere are  harvested  in  our  late  winter  and  early  spring,  when  the  northern  supplies 
of  certain  things  are  running  low.  Hence  there  is  important  trade  between  the  two 
hemispheres,  places  in  each  hemisphere  being  benefited  because  their  crops  ripen  in 
the  cold  season  of  the  other. 

Warmest  and  coldest  months.  Since  the  northern  hemisphere 
receives  most  heat  at  the  time  of  summer  solstice,  and  least  at  the 
time  oi  winter  solstice,  it  would  seem  at  first  that  these  dates,  respec- 
tively, should  be  the  times  of  greatest  heat  and  cold;  but  this  is  not  the 


42  CLIMATIC  FACTORS:    TEMPERATURE 

case.  Again,  since  corresponding  latitudes  in  the  two  hemispheres 
are  being  heated  equally  at  the  time  of  the  equinoxes,  it  would  seem, 
at  first,  that  corresponding  latitudes  in  the  two  hemispheres  should 
have  the  same  temperature  at  these  times;  but  this,  again,  is  not  the 
case.  In  our  own  latitudes,  for  example,  March  2  ist  (vernal  equinox) 
is  much  colder  than  September  2 2d  (autumnal  equinox). 

The  explanation  of  these  conditions  is  found  in  the  fact  that 
the  temperature  of  any  given  place  at  any  given  time  does  not  depend 
entirely  on  the  amount  of  heat  received  from  the  sun  at  that  time. 
In  our  latitudes-  the  soil,  rocks,  lakes,  and  rivers  receive  more  heat 
during  the  long  days  of  summer  than  is  lost  during  the  short  nights. 
At  the  end  of  summer,  therefore,  heat  has  been  stored  up  in  them.' 
At  this  time  of  year,  the  northern  hemisphere  has  a  temperature 
higher  than  that  which  it  would  have  if  it  depended  entirely  on  the 
heat  received  from  the  sun  each  day.  On  the  other  hand,  the  tem- 
perature at  the  time  of  early  spring  is  lower  than  that  which  the  daily 
heating  would  seem  to  produce,  because  the  cold  of  the  winter  just 
past  has  not  been  altogether  overcome.  Some  of  the  snow  and  some 
of  the  ice  of  lakes,  ponds,  streams,  and  soils,  in  middle  and  high 
latitudes,  is  still  unmelted.  The  snow  and  ice  keep  the  lower  part 
of  the  air  cool. 

For  similar  reasons,  the  summer  solstice  is  not  the  hottest  time 
of  year.  The  time  of  greatest  heat  lags  behind  the  time  of  greatest 
heating.  In  middle  latitudes  the  lag  is  about  a  month;  but  it  is  more 
over  oceans  than  over  lands,  because  land  is  heated  and  cooled  more 
readily  than  water.  For  this  reason  places  near  bodies  of  water  usual- 
ly have  later  and  colder  springs  than  places  not  so  situated.  Under 
such  conditions,  April  in  the  northern  hemisphere  may  be  as  cold  as 
November.  In  the  same  way,  the  time  of  greatest  cold  does  not  come 
till  after  the  time  of  least  heating. 

In  Tropical  Latitudes 

The  seasons  in  lovv  latitudes  are  unlike  our  own.  At  the  equator, 
the  sun's  rays  are  vertical  twice  each  year  —  at  the  times  of  the 
equinoxes.  Twice  a  year,  too,  the  sun 's  rays  are  vertical  23^°  from 
the  equator,  once  to  the  north  and  once  to  the  south.  The  equator, 
therefore,  has  two  seasons,  occurring  at  the  time  of  our  spring  and 
autumn,  which  are  somewhat  warmer  than  two  other  seasons  occur- 
ring at  the  time  of  our  summer  and  winter.  The  variations  in 
temperature  are  much  less  than  in  middle  latitudes,  for  the  length 


CONTRASTS  OF   SEASONS  43 

of  day  and  night  never  varies  at  the  equator,  and  does  not  vary  much 
in  any  part  of  the  tropics.  The  angle  of  the  sun's  rays,  too,  varies 
less  than  with  us.  At  the  equator,  therefore,  there  are  four  di- 
visions of  the  year,  but  their  differences  of  temperature  are  slight. 
Toward  the  margins  of  the  tropical  zone,  the  variations  of  tem- 
perature are  greater  than  at  the  equator,  but  far  less  than  in  middle 
latitudes.  In  much  of  the  tropical  zone,  wet  seasons  alternate  with 
dry  ones,  and  in  such  places,  differences  in  moisture  are  more  im- 
portant than  differences  in  temperature. 

In  High  Latitudes 

In  high  latitudes,  the  seasons  are  still  different.  About  latitude 
60°,  for  example,  the  differences  in  the  seasons  are  similar  to  those 
of  the  central  part  of  the  United  States,  except  that  they  are  greater, 
because  of  the  greater  variation  in  the  length  of  day  and  night.  In 
latitude  63°,  the  longest  day  of  summer  and  the  longest  night  of 
winter  are  about  20  hours  each,  as  compared  with  a  little  over  15 
hours  in  latitude  40°.  The  long  nights  of  winter  in  latitude  63° 
mean  much  lower  temperatures  than  in  latitude  40°  at  that  season. 
On  the  other  hand,  the  long  hours  of  sunshine  in  summer  make 
it  possible,  in  favored  localities,  to  grow  crops  as  far  north  as  latitude 
60°,  even  where  it  is  only  four  months  from  snow  to  snow. 

In  latitude  75°  N.,  which  may  be  taken  as  typical  of  polar  regions, 
there  are  four  natural  divisions  of  the  year,  one  (summer)  when 
daylight  is  continuous,  one  (winter)  when  darkness  is  continuous, 
one  (spring)  when  there  is  alternating  day  and  night,  with  the  days 
lengthening,  and  one  (autumn)  when  there  is  alternating  day  and 
night,  with  the  nights  lengthening.  The  lengths  of  the  seasons 
defined  in  this  way  are  not  the  same. 

There  is  a  common  notion  that  in  polar  regions  there  is  a  day  of  six  months 
and  a  night  of  six  months  each  year,  but  this  is  not  correct.  There  is  a  six-month 
day  and  a  six-month  night  at  the  poles  only.  In  latitude  78°,  about  half  way  between 
the  pole  and  the  polar  circle,  there  is  continuous  daylight  and  continuous  darkness 
for  periods  of  about  four  months  each.  In  latitude  70°  the  periods  of  continuous 
darkness  and  of  continuous  Ught  are  two  months  each,  and  so  on  down  to  24  hours 
at  the  polar  circle. 

Though  the  name  summer  may  be  applied  to  one  part  of  the  year 
in  high  latitudes,  places  north  of  latitude  6o°-6s°  are  not  warm  enough 
in  summer  for  the  growth  of  cereal  crops.  Vegetation  is  confined  to 
grasses,  stunted  shrubs,  lichens,  and  mosses. 


44  CLIMATIC  FACTORS:    TEMPERATURE 

Relation  of  Temperature  and  Altitude 

High  altitudes  are  colder  than  low  levels  in  the  same  region, 
(i)  because  the  air  is  thinner,  and  (2)  because  it  contains  less  water 
vapor,  carbon  dioxide,  and  dust.  For  these  reasons  it  absorbs  less 
heat  from  the  direct  rays  of  the  sun,  and  less  of  that  radiated  from 
below.  The  temperature  of  the  air  on  top  of  a  mountain  may  be 
much  lower  than  the  temperature  of  the  air  at  its  base,  in  spite  of  the 
fact  that  insolation  is  much  greater  in  the  former  position. 

The  average  decrease  of  temperature  is  about  1°  F.  for  each  330 
feet  of  rise,  or  16°  for  each  mile,  for  the  altitudes  where  observations 
have  been  taken.  One  mile  of  ascent,  therefore,  means  about  the 
same  decrease  of  temperature  as  a  journey  of  1,000  miles  (about  15° 
of  latitude)  toward  the  poles.  Tropical  highlands,  like  those  of 
Mexico  or  Bolivia,  in  latitudes  18°  to  19°  N.  and  S.  respectively, 
are  cooler  than  some  places  at  sea-level  in  middle  latitudes.  For 
this  reason,  some  countries  in  the  tropics  can  produce  not  only 
tropical  crops,  but  also  those  characteristic  of  other  regions,  and  by 
living  at  the  higher  elevations,  the  people  may  escape  the  uncomfort- 
able heat  of  tropical  lowlands.  In  middle  latitudes  also  vegetation 
varies  with  the  altitude.  Thus,  in  the  low  mountains  of  Pennsylvania, 
the  ridges  bear  coniferous  trees  (pines,  etc.),  sugar  maples,  and  similar 
types,  while  the  valleys  between  have  the  honey  locust,  gum,  and 
walnut,  which  need  a  warmer  climate. 

The  low  temperatures  of  certain  mountains  and  high  plateaus  of 
the  middle  zones  do  not  favor  dense  populations.  On  the  other  hand, 
the  cool  climates  of  various  high  lands  in  the  tropics  have  favored 
white  settlements.  During  the  hot  summer  months  the  capital  of 
India  was  transferred  each  year  from  Calcutta  (the  capital  until 
191 1),  near  sea-level,  to  Simla  in  the  Himalayas,  at  an  elevation  of 
7,000  feet.  Certain  elevated  places  in  the  Philippines,  like  Baguio, 
the  summer  capital,  will  have  increasing  importance  as  health  and 
pleasure  resorts  during  the  hot  period. 

The  difference  in  vegetation  and  in  human  conditions  between 
the  sunny  and  shady  slopes  of  mountains  is  striking  in  many  cases. 
Thus  at  a  place  near  Zermatt,  in  the  Alps,  barley  and  rye  are  grown 
on  a  sunny  southern  slope  6,900  feet  above  sea-level,  while  a  few 
hundred  yards  away,  northern  slopes,  even  below  the  level  of  the 
grain  tields,  have  arctic-alpine  vegetation  and  snow-banks.  In  some 
of  the  valleys  in  the  Alps,  most  of  the  people  live  on  the  sunny  slopes. 


CHARTING   TEMPERATURE   DATA  45 

Where  mountains  are  covered  by  snow  throughout  the  year,  their  surfaces  are 
never  warmed  above  a  tetnperaticre  of  32°  F.,  the  melting  temperature  of  snow.  All 
the  heat  received  beyond  that  necessary  to  raise  them  to  this  temperature  is  spent 
in  melting  and  evaporating  snow,  not  in  raising  the  temperature  of  its  surface. 
Yet  in  spite  of  the  freezing  temperature,  travellers  over  the  snow-fields  may  be 
sun-burned,  as  if  exposed  to  midsummer  sun  at  lower  altitudes.  Part  of  this  effect 
is  due  to  the  greater  intensity  of  insolation  at  higher  altitudes,  and  part  of  it  to  the 
fact  that  snow  reflects  heat  much  as  water  does  (p.  40). 


Representation  of  Temperature  on  Maps 

It  is  important  to  have  some  means  by  which  temperatures  in 
different  places  and  at  different  times  may  be  studied  readily.  For 
large  areas  it  is  most  convenient  to  have  the  temperatures  shown  on 
maps.  Maps  showing  temperatures  are  thermal  maps.  On  such  maps 
temperatures  and  their  distribution  commonly  are  shown  by  lines, 
each  of  which  connects  points  having  the  same  temperature.  Such 
lines  are  isotherms,  and  maps  showing  isotherms  are  isothermal  maps. 
A  line  connecting  places  having  the  same  average  annual  temperature 
is  an  annual  isotherm.  Lines  connecting  places  of  the  same  average 
seasonal  or  monthly  temperature  are  seasonal  or  monthly  isotherms. 

Fig.  24  shows  annual  isotherms.  The  map  does  not  give  exact 
average  temperatures  for  places  between  the  lines,  but  tempera- 
tures for  such  places  can  be  estimated  from  the  map.  At  the 
extreme  north  there  is  the  isotherm  of  0°  F.,  which  barely  touches 
North  America.  The  average  annual  temperature  of  places  on 
this  line  is  0°  F.  The  isotherm  of  10°  F.  lies  south  of  the  isotherm 
of  0°  F.  The  average  temperature  of  places  between  these  two  lines 
is  more  than  0°,  and  less  than  10°.  South  of  the  isotherm  of  10° 
follow,  in  order,  the  isotherms  of  30°,  50°,  60°,  and  70°.  The  lowest 
isotherm  shown  on  the  chart  in  the  southern  hemisphere  is  that  of 
30°,  lying  south  of  all  lands  except  Antarctica.  The  latitude  of  this 
isotherm  corresponds  nearly  to  the  latitude  of  the  isotherm  of  30° 
in  the  northern  hemisphere.  Next  toward  the  equator  from 
the  southern  isotherm  of  30°  is  the  isotherm  of  50°,  followed  by  those 
of  60°  and  70°.  Thus  the  map  shows  a  relation  between  latitude 
and  annual  temperatures,  the  highest  temperatures  being  near  the 
equator. 

Annual  isotherms  do  not  show  all  we  may  want  to  know  about 
the  temperature  conditions  of  a  place.  An  annual  isotherm  of  50°  F., 
for  example,  does  not  tell  us  whether  the  temperature  is  about  50°  F. 


46 


CLIMATIC   FACTORS:    TEMPERATURE 


ISOTHERMAL   CHARTS  47 

all  the  time,  or  whether  it  is  80°  F.  in  summer  and  20°  in  winter. 
Seasonal  and  monthly  isotherms  are  of  more  significance  in  con- 
nection with  crops,  and  give  a  better  idea  of  the  temperature  condi- 
tions of  a  place.  This  may  be  illustrated  by  the  fact  that  the  annual 
isotherm  of  New  York  is  about  the  same  as  that  of  southern  England, 
while  the  summer  isotherm  of  the  former  place  is  more  than  10° 
warmer  than  that  of  the  latter.  Since  summer  temperatures  are  the 
most  important  for  crops  and  for  many  human  activities,  the  difference 
of  more  than  10°  in  that  season  is  enough  to  make  New  York  and 
southeastern  England  quite  unlike  in  many  respects.  Again,  San 
Francisco  and  St.  Louis  have  the  same  mean  annual  temperature; 
but  the  January  average  is  only  10°  lower  than  the  July  average  at  San 
Francisco,  while  it  is  45°  lower  at  St.  Louis.  Range  of  temperature  is, 
therefore,  important.  The  annual  range  of  temperature  for  Quito, 
Ecuador,  is  1°  F. ;  that  is,  the  warmest  month  is  only  about  1°  warmer 
than  the  coolest.  For  San  Diego,  Cal.,  the  range  is  16°  F,;  for  St. 
Paul,  Minn.,  60°;  for  Yakutsk,  northeastern  Siberia,  100°. 

Fig.  25  shows  the  isotherms  for  January.  On  this  chart  corres- 
ponding isotherms  are  farther  south  than  on  the  chart  of  annual 
isotherms.  Thus  the  isotherm  of  0°  F,  (  —  17.78°  C.)  in  the  northern 
hemisphere  runs  through  central  Asia,  instead  of  lying  north  of  it, 
and  the  isotherm  of  60°  is  everywhere  south  of  latitude  40°,  instead 
of  being  partly  north  of  it,  as  in  Fig,  24.  At  this  time  of  the  year, 
the  sun  is  shining  vertically  south  of  the  equator.  This  seem'='  to  be 
a  sufficient  reason  for  the  change. 

Fig.  26  shows  the  isotherms  for  July.  All  isotherms  are  farther 
north  than  the  corresponding  ones  on  either  of  the  other  charts.  Thus 
the  isotherm  of  50°  in  the  northern  hemisphere  is  about  where  the 
isotherm  of  20°  was  in  January  (Fig,  25), 

Comparing  Figs.  25  and  26,  it  is  seen  that  the  difference  of  tem- 
perature between  January  and  July  is  much  greater  in  high  latitudes 
than  in  low.  Thus  in  the  southern  part  of  Hudson  Bay  there  is  70° 
difference  between  January  and  July;  at  Lake  Erie,  about  45°;  in 
Florida,  about  20°;  and  near  the  equator  in  South  America,  less  than 
10°.  The  same  charts  show  that  the  difference  is  greater  in  the 
interiors  of  continents  than  on  coasts  or  over  the  sea  in  the  same 
latitude.  Thus  in  the  interior  of  North  America,  west  of  Hudson 
Bay,  the  difference  is  about  80°,  while  on  the  coast  of  Alaska  it  is 
only  about  30°.  These  conditions  bear  out  the  conclusions  already 
reached,  (i)  that  the  difference  in  the  amounts  of  heat  received  at 


48 


CLIMATIC   FACTORS:   TEMPERATURE 


ISOTHERMAL  CHARTS 


49 


u 
PQ 


3 


o 


so  CLIMATIC   FACTORS:    TEMPERATURE 

difiFerent  seasons  is  greater  in  high  latitudes  than  in  low  latitudes,  and 
(2)  that  land  heats  and  cools  more  readily  than  water.  . 

The  courses  of  isotherms,  (i)  The  isotherms  are  roughly 
parallel  to  the  parallels  of  latitude.  Some  of  them  are  very  irregular, 
it  is  true,  but  the  east-west  direction  is  the  most  common  one.  This 
shows  some  relation  between  the  courses  of  isotherms  and  latitude; 
but  since  the  isotherms  do  not  follow  the  parallels  exactly,  it  is  clear 
that  latitude  is  not  the  only  thing  which  determines  their  position. 

(2)  Figs.  25  and  26  show  that  the  isotherms  are  least  crooked 
where  there  is  little  land,  and  most  crooked  where  there  is  much  land. 
This  suggests  that  the  land  and  water  have  something  to  do  with 
their  positions.  There  are  various  irregularities  in  the  isotherms  on 
land  that  do  not  appear  on  the  sea.  Thus,  on  the  January  chart, 
there  is  an  area  in  South  Africa,  and  another  in  Australia,  surrounded 
by  the  isotherm  of  90°,  and  in  July  there  are  similar  areas  in  North 
America,  northern  Africa,  and  southern  Asia.  All  of  these  areas  are 
on  land.  These  facts  tend  to  confirm  the  conclusion  that  the  sea 
ind  the  land  influence  the  position  of  the  isotherms. 

Following  this  idea  further,  it  is  seen  that  some  of  the  isotherms 
of  January  bend  somewhat  abruptly  toward  the  equator  in  passing 
from  water  to  land,  and  toward  the  pole  in  passing  from  land  to 
water.  Thus  the  isotherm  of  30°  in  the  northern  hemisphere  turns 
to  the  south  where  it  reaches  North  America,  and  again  on  the  coast 
of  Europe.  In  the  southern  hemisphere,  the  isotherms  of  80°  and  70° 
make  abrupt  turns  at  the  west  coast  of  Africa,  and  the  isotherm  of 
70°  near  the  west  coast  of  South  America.  These  bends  at  the  coasts 
give  further  support  to  the  conclusion  that  the  distribution  of  land 
ind  water  has  something  to  do  with  the  position  of  isotherms. 

It  has  been  noted  already  (p.  40)  that  the  land  is  heated  and 
cooled  more  readily  than  the  sea,  and  is  therefore  colder  in  winter 
and  warmer  in  summer.  The  January  isotherm  of  30°  in  the  northern 
hemisphere  bends  toward  the  equator  in  crossing  the  northern  con- 
tinents, because  the  land  is  cooler  than  the  water  in  the  same  latitude, 
at  this  time  of  year.  In  the  southern  hemisphere,  where  it  is  summer, 
the  isotherms  bend  toward  the  pole  on  reaching  the  land,  because  the 
land  is  warmer  than  the  sea  in  the  same  latitude. 

The  chart  of  the  July  isotherms  leads  to  the  same  conclusion. 
On  this  chart,  isotherms  crossing  the  northern  continents  bend 
poleward  on  the  land,  while  those  crossing  the  southern  continents 
bend  equatorward.     This  is  the  season  when  the  lands  of  the  northern 


ISOTHERMAL   CHARTS  51 

hemisphere  are  warmer  than  the  seas  of  the  same  latitude,  and  when 
the  lands  of  the  southern  hemisphere  are  cooler  than  the  seas. 

The  irregularities  of  the  isotherms  of  the  northern  hemisphere 
in  July  are  much  greater  than  those  of  the  southern  hemisphere 
in  January  (summer  in  the  southern  hemisphere).  This  is  prob- 
ably because  there  is  much  more  land  in  the  northern  hemisphere 
than  in  the  southern,  and  the  larger  land  areas  have  a  greater  efifect 
on  the  isotherms  than  the  smaller  ones. 

(3)  There  are  some  features  of  the  isothermal  lines  which  are 
not  explained  by  latitude,  or  by  the  distribution  of  continents  and 
oceans.  Thus  the  bends  of  the  isotherms  are  not  as  pronounced  on 
the  east  sides  of  the  continents  as  on  the  west.  This  is  shown  by 
Figs.  25  and  26.  Again,  traced  eastward,  the  January  isotherm  of  50° 
bends  southward  near  the  west  coast  of  North  America  more  sharply 
on  the  land,  while  on  the  eastern  side  of  the  continent  it  bends  north- 
ward on  the  sea,  not  on  the  land.  Such  peculiarities  may  be  explained 
by  the  winds.  The  prevailing  winds  in  the  middle  latitudes  of  North 
America  are  from  the  west.  These  winds  tend  to  carry  the  tempera- 
ture of  the  sea  (warmer  in  winter)  over  to  the  land  on  the  western 
side  of  the  continent  (Fig.  25),  and  the  temperature  of  the  land 
(cooler  in  winter)  over  to  the  sea,  on  its  eastern  side.  This  explains 
the  bends  of  the  isotherm  of  50°,  for  example,  near  the  coasts  in  the 
northern  hemisphere  in  January.  Coastal  lands  on  the  western  sides 
of  continents  in  middle  latitudes  tend  to  have  temperatures  like 
those  of  the  neighboring  ocean. 

(4)  The  great  bend  in  the  January  isotherm  of  30°  in  the  North 
Atlantic  is  due  to  a  northeastward  movement  of  warm  ocean  water 
in  the  direction  of  the  pronounced  loop  of  the  isotherm.  Ocean 
currents  are  therefore  a  fourth  cause  of  the  irregularities  of  isotherms. 
The  amount  of  heat  carried  northward  by  the  ocean  currents  of 
the  Atlantic  and  Pacific  is  very  large.  It  has  been  estimated  that 
the  temperature  of  the  British  Isles  and  Norway  is  raised  several 
degrees  by  the  warm  poleward  movement  of  waters  in  the  North 
Atlantic.  The  temperature  of  the  land  is  raised  by  this  water, 
because  the  air  over  the  warm  ocean  water  is  warmed  and  then 
blown  over  the  land. 

The  milder  climate  of  northwestern  Europe,  as  compared  with 
northeastern  North  America,  is  not  due  wholly  to  the  northward 
movement  of  warm  water.  Even  without  such  movement,  the 
tlimate  of  northwestern   Europe   would   be   somewhat   warmer  in 


52  CLIMATIC   FACTORS:    TEMPERATURE 

winter  than  that  of  northeastern  North  America  in  the  same  latitudes, 
because  the  ocean,  from  which  the  winds  of  winter  blow  to  north- 
western Europe,  still  would  be  warmer  than  interior  North  America, 
whence  the  prevailing  winds  blow  to  the  eastern  coast  of  that  conti- 
nent. 

There  are  some  other  less  important  causes  of  irregularities  in 
the  isotherms.  Thus  a  basin  region,  shut  in  by  mountains,  gets 
hotter  in  summer  than  a  region  not  so  surrounded.  Again,  there 
is  less  evaporation  from  a  dry  surface  than  from  a  moist  one,  and 
since  evaporation  cools  the  surface,  a  dry  surface  will  be  warmer 
than  a  moist  one,  if  other  conditions  are  the  same.  The  color  of  the 
soil,  the  presence  or  absence  of  vegetation,  and  other  things,  also 
affect  the  absorption  and  radiation  of  heat.  The  high  temperature 
in  the  southwestern  part  of  the  United  States  in  July  (Fig.  26)  is 
accounted  for  partly  by  the  fact  that  the  region  is  somewhat  shut 
in  by  mountains,  and  has  a  dry,  sandy  soil  but  scantily  covered  with 
vegetation. 

Altitude  affects  temperature,  as  already  explained,  but  isother- 
mal charts  show  no  relation  between  isothermal  lines  and  surface 
relief.  The  reason  is  that  isothermal  lines  are  represented  on  maps 
as  if  they  were  at  sea-level.  This  is  done  by  making  allowance  for 
altitude  at  the  average  rate  of  1°  F.  for  about  330  feet.  Thus  if 
the  temperature  of  a  place  at  an  altitude  of  3,300  feet  is  60°,  it  is 
put  down  on  the  chart  as  70°  (60°+ 10°).  Isothermal  charts,  there- 
fore, are  intended  to  show  the  temperature  as  it  would  be  if  the  land 
were  at  sea-level. 

Ranges  of  Temperature 

Daily  range.  The  temperature  of  a  day  when  the  sun  shines  is 
generally  higher  than  the  temperature  of  the  night.  The  difference 
is  as  much  as  40°  or  50°  F.  in  many  places,  and  as  much  as  70°  in 
some.  The  daily  range  of  temperature  of  air  over  the  ocean  is  much 
less  than  over  the  land;  other  things  equal,  less  at  high  altitudes  than 
at  low  altitudes,  and  less  in  moist  regions  than  in  dry  ones. 

The  greatest  importance  of  daily  range  of  temperature  is  in  con- 
nection with  the  growth  of  crops.  Since  many  plants,  including 
many  food  plants,  are  injured  or  killed  by  a  freezing  temperature 
(commonly  called  "frost"),  they  are  restricted  to  regions  where 
the  temperature  during  the  growing  season  does  not  fall  as  low  as 
32°  F. 


FROSTS  AND    CROPS  53 

The  danger  of  "frost"  at  night  varies  with  local  conditions,  as  (i)  altitude,  (2) 
exposure,  (3)  character  of  the  soil,  and  (4)  nearness  to  water  bodies.  Valley 
bottoms  have  frosts  earlier  in  the  autumn  than  neighboring  hillsides,  because  the 
colder,  heavier  air  moves  down  slopes  and  accumulates  in  low  places.  The  great 
coffee  plantations  of  Sao  Paulo,  Brazil,  the  oHve  and  fig  trees  of  Italy  and  Istria, 
the  orange  and  peach  orchards  of  California,  and  the  vineyards  in  the  Rhine  Valley 
and  in  the  south  of  France  are  found  largely  on  hillsides. 

Northern  slopes  are  more  subject  to  frosts  than  southern  ones,  because  the 
latter  are  warmed  more  by  day  and  hence  must  cool  more  at  night  before  a  freezirg 
temperature  is  reached.  Sandy  soils  are  more  liable  to  frost  than  clay  soils  situated 
similarly,  for  the  reason  that  clay  soils  are  usually  wetter.  The  air  above  them 
contains  more  moisture,  and  so  cools  less  readily.  The  condensation  of  moisture 
sets  free  heat  and  so  checks  further  cooling.  Of  two  crops  on  the  same  farm,  one 
on  clay  soil,  the  other  on  sandy  soil,  the  one  may  be  untouched  by  "frost"  on  a 
night  when  the  other  is  injured  seriously.  Places  near  water  bodies,  and  in  their 
lee  (i.  e.,  on  the  side  toward  which  the  wind  blows  from  the  water)  have  their 
temperatures  influenced  by  the  temperature  of  the  water.  Frosts  at  night  in 
autumn  are  somewhat  less  common  in  such  situations.  The  effect  of  large  water 
bodies  is  seen  in  the  location  of  important  fruit  districts  on  the  lee  (east)  shore  of 
Lake  Michigan,  and  on  the  lee  (southeast)  shores  of  Lakes  Erie  and  Ontario.  A 
similar  influence  affects  the  important  fruit  and  trucking  industry  of  the  peninsula 
between  Delaware  and  Chesapeake  bays.  Frosts  during  the  growing  season  are, 
in  some  cases,  so  destructive  as  to  amount  almost  to  national  disasters.  A  frost 
in  the  late  spring,  after  corn  is  well  started,  or  in  early  autumn,  before  it  is  ripe, 
may  reduce  the  crop  of  good  corn  by  millions  of  bushels.  When  freezing  tem- 
peratures extend  into  regions  usually  free  from  them,  they  do  great  damage  to 
fruit,  as  to  orange  groves  in  Florida.  A  disastrous  frost  in  December,  1894, 
affected  this  region. 

The  economic  importance  of  frost  is  so  great  that  the  federal  government  has 
given  much  attention  to  methods  for  protecting  p>erishable  crops,  and  one  of  the 
most  valuable  services  of  the  Weather  Bureau  is  the  sending  out  of  frost  warnings 
which  give  the  farmers  of  the  country  anywhere  from  6  to  24  hours  to  make  prepara- 
tion for  protection.  In  this  way,  millions  of  dollars'  worth  of  crops  are  saved  every 
year.  The  cost  of  protection  for  several  consecutive  nights  may  not  equal  i  per 
cent  of  the  value  of  the  crop  saved. 

The  average  daytime  temperature  during  the  growing  season, 
and  the  number  of  days  when  the  temperature  is  above  a  given  point, 
are  important  matters,  since  most  plants  require,  for  growth,  a  tem- 
perature well  above  32°  F. 

The  daily  range  of  temperature  is  also  important  to  human  beings, 
especially  where  the  days  are  hot.  Thus  in  desert  regions  the  heat 
of  midday  may  be  much  above  100°  F.;  but  night  temperatures  in 
the  same  place  may  be  as  low  as  45°  or  50°  F.,  making  restful  sleep 
possible. 

It  is  the  daily  range  of  temperature  which  accounts  partly  for  the 
invigorating  effects  of  a  vacation  in  the  mountains. 


54  CLIMATIC   FACTORS:    TEMPERATURE 

Seasonal  range.  The  seasonal  range  of  temperature  is  aflfected 
by  (i)  latitude,  (2)  position  with  reference  to  land  and  sea,  (3)  pre- 
vailing winds,  and  (4)  the  presence  of  snow. 

(i)  The  seasonal  range  of  temperature  increases  with  the  latitude 
(compare  Figs.  25  and  26),  because  the  yearly  variation  of  insola- 
tion increases  with  the  latitude.  San  Diego  and  St.  Paul  (p.  47)  are 
examples.  In  latitudes  higher  than  that  of  St.  Paul  the  range  is  still 
greater. 

(2)  Islands  and  coasts  have  a  smaller  range  than  continental  in- 
teriors in  the  same  latitude,  because  the  range  of  sea  temperature  is 
less  than  the  range  of  land  temperature  (Figs.  25  and  26).  St.  Louis 
and  San  Francisco  (p.  47)  are  examples. 

(3)  A  coast  to  which  the  prevailing  winds  blow  from  the  ocean 
has  a  less  range  of  temperature  than  a  coast  to  which  the  prevailing 
winds  blow  from  the  land.  Thus  the  range  of  temperature  is  less 
on  the  Pacific  coast  of  the  United  States  than  on  the  Atlantic  in  the 
same  latitude  (Figs.  25  and  26),  the  winds  being  chiefly  from  the  west 
in  both  cases. 

(4)  The  presence  of  snow  during  the  warm  season,  as  in  high 
latitudes  and  high  mountains,  prevents  a  high  temperature,  even 
though  insolation  is  strong  (p.  45).  In  the  cold  season,  snow  also 
tends  to  reduce  the  temperature  of  the  lower  air  by  reflecting  a 
certain  amount  of  insolation  which  might  otherwise  help  to  warm 
the  land,  and  so  the  layers  of  air  in  contact  with  it.  On  the  other 
hand,  snow  lessens  the  range  of  temperature  of  the  soil  beneath  it, 
for  snow  checks  radiation  from  the  soil,  and  prevents  it  from  being 
warmed  by  the  direct  rays  of  the  sun.  By  preventing  alternate  freez- 
ing and  thawing  of  the  soil,  snow  is  important  to  many  plants,  as,  for 
example,  winter  wheat  and  clover. 

Importance  of  temperature  ranges.  The  annual  range  of  tem- 
perature affects  all  industries  connected  with  the  soil.  In  general,  the 
temperature  of  most  importance  to  vegetation  is  the  lowest  or  mini- 
mum temperature.  For  example,  the  palm-tree  does  not  thrive  where 
frosts  occur;  hence  its  natural  distribution  is  limited  to  places  where 
the  lowest  temperature  of  the  year  is  above  32°  F.  Peach-trees,  unless 
protected,  are  injured  by  temperatures  below — 15°  F.  if  they  last  long, 
and  if  such  temperatures  come  often,  peaches  cannot  be  grown.  Fo;? 
most  crops,  as  corn,  cotton,  rice,  tobacco,  sugar  cane,  fruits,  ancT 
vegetables,  the  length  of  time  without  freezing  temperatures  (the 
growing  season)  is  a  critical  factor  affecting  their  distribution. 


QUESTIONS  55 

Unseasonably  low  temperatures  may  destroy  crops  not  only  for 
that  year,  but  in  some  cases  for  years  to  come.  Thus,  early  m 
October,  1906,  a  temperature  which  was  in  places  13°  below  freez- 
ing killed  hundreds  of  thousands  of  peach-trees  in  western  Michigan. 
Peach-trees  stand  much  lower  temperatures  in  winter  without  injury, 
but  this  freezing  temperature  came  before  the  trees  were  ready  for  it. 


Questions 

1.  From  what  sources,  besides  the  sun,  does  the  earth's  surface  receive  heat? 

2.  What  temperature  Centigrade  corresponds  to  45°  F.?     To  —  45°  F.? 

3.  Make  a  rule  for  changing  degrees  F.  to  degrees  C,  and  vice  versa. 

4.  The  earth  is  probably  not  getting  warmer,  in  spite  of  the  fact  that  it  is 
receiving  heat  all  the  time  from  the  sun.     Why? 

5.  On  June  21st,  in  latitude  40°  N.,  which  would  receive  more  heat,  (i)  a 
horizontal  surface,  or  (2)  a  vertical  surface  of  equal  area  facing  south?  On  Sep- 
tember 2ist?     Draw  diagrams  to  illustrate  answers. 

6.  For  each  of  the  various  ways  of  heating  a  house,  by  (i)  open  fire,  (2)  stoves, 
(3)  hot-air  furnace,  (4)  steam,  and  (5)  hot  water,  which  process  of  heat  distribution 
(radiation,  convection,  conduction)  is  most  important? 

7.  In  what  way  may  satisfactory  ventilation  of  a  heated  room  be  secured? 

8.  Why  does  snow  mixed  with  dirt  melt  more  rapidly  than  clean  snow.'- 

9.  How  does  a  lake  tend  to  modify  the  temperature  of  the  surrounding  land 
by  day?     By  night?     In  summer?     In  winter?     Explain  each. 

10.  Explain  each  important  curve  in  the  January  isotherm  of  10°  F.,  northern 
hemisphere  (Fig.  25). 

11.  (i)  Compare  and  contrast  the  average  January  and  July  temperatures  on 
the  east  and  west  coasts  of  the  United  States  at  the  fortieth  parallel  (Figs.  25  and 
26).     (2)  Explain  the  differences. 

12.  Why  are  the  average  annual  temperatures  over  tropical  lands  higher  than 
those  over  tropical  seas? 

13.  Where  do  the  highest  July  temperatures  occur  (Fig.  26)?  Why  there? 
The  lowest  January  temperatures  (Fig.  25)?     Whj^? 

14.  Compare  and  contrast  the  seasonal  range  of  temperature  in  the  middle 
latitudes  of  the  two  hemispheres  (Figs.  25  and  26).     Why  the  difference? 

15.  Of  two  cities,  St.  Paul  and  Key  West,  one  has  an  average  daily  range  ir. 
temperature  twice  as  great  as  the  other.    Which  has  the  greater?     Reasons? 

16.  Why  is  the  average  annual  temperature  higher  in  cities  than  in  the  sur- 
rounding country?  Why  is  the  daily  range  of  temperature  smaller  in  cities  than 
in  the  country? 

17.  What  is  the  length  of  the  growing  season  in  mountains,  as  compared  with 
neighboring  plains?    Why? 


CHAPTER  VI 
CLIMATIC   FACTORS:     MOISTURE 

Importance  of  Atmospheric  Moisture 

We  cannot  see  or  smell  or  feel  water  vapor,  though  air  with  much 
Water  vapor  has  a  different  feeling  from  air  with  little. 

The  presence  of  vapor  in  the  air  may  be  proved  in  various  ways. 
Drops  of  water  often  appear  on  the  outside  of  a  pitcher  of  ice-water 
in  summer,  and  cold  window  panes  often  have  "steam"  on  them  in 
winter.  In  each  case  the  water  came  from  the  air.  Water  vapor 
often  condenses  into  water  on  the  surface  of  dust  particles  in  the  air. 
Great  numbers  of  these  water-covered  particles  high  in  the  air  form 
clouds,  from  which  rain  may  fall  if  the  drops  become  heavy  enough. 

Water  vapor  is  lighter  than  dry  air;  that  is,  a  cubic  foot  of  it 
weighs  less  than  a  cubic  foot  of  dry  air  at  the  same  temperature  and 
under  the  same  pressure.  Water  vapor  in  the  air  displaces  some  of 
the  oxygen  and  nitrogen,  and  therefore  makes  the  air  lighter. 

The  moisture  of  the  air  is  no  less  important  than  oxygen  and 
carbon  dioxide  to  animals  and  plants,  for  without  it  no  life  could 
exist  on  the  land.  It  furnishes  the  rain  and  the  snow  which  supply 
all  springs  and  rivers,  and  it  serves  a  most  important  function  in 
connection  with  temperature,  as  already  stated  (p.  32).  It  increases 
the  average  temperature  at  the  bottom  of  the  atmosphere,  and  reduces 
the  extremes  of  heat  and  cold  which  would  exist  if  the  air  were  alto- 
gether dry.  This  is  shown  by  the  fact  that  dry  regions  have  greater 
ranges  of  temperature  than  moist  ones  in  similar  latitudes  and  alti- 
tudes. Moisture  from  the  air  also  acts  with  the  oxygen  and  with 
changes  of  temperature  in  the  breaking  up  of  rocks  and  the  formation 
of  soil  from  them  (p.  162). 

Evaporation 

Sources  of  water  vapor.  Water  left  in  an  open  dish  disappears 
slowly,  and  muddy  roads  and  wet  pavements  become  dry  after  the 
rain  ceases.     The  water  evaporates;  that  is,  it  disappears  in  the  form 

56 


SOURCES   OF   WATER   VAPOR  57 

of  vapor.  Vapor  is  passing  from  all  moist  surfaces  into  the  air  all  the 
time.  Evaporation  also  takes  place  from  snow  and  ice,  even  at  tem- 
peratures far  below  that  of  melting.  Explorers  in  Arctic  regions 
say  that  moist  garments  left  on  the  snow  during  a  clear  night  may  be 
dry  in  the  morning,  even  with  a  temperature  of  —  40°  F,  The  mois- 
ture in  the  garments  freezes,  and  the  ice  evaporates. 

All  animals  breathe  out  w^ater  vapor  into  the  air.  This  is  seen 
on  very  cold  days  when  the  water  vapor  of  the  breath  condenses,  and 
so  becomes  visible.  The  water  breathed  out  into  warm  air  is  not 
seen  because  it  does  not  condense.  Growing  plants  also  give  out 
moisture,  the  amount,  in  many  cases,  being  very  great. 

A  thrifty  sunflower  plant,  during  its  life  of  140  days,  gave  off  125  pounds  of 
water.  Grass  was  found  to  give  off  its  own  weight  of  water  every  24  hours,  in  hot 
weather.  This  meant,  where  the  measurement  was  made,  6)4  tons  per  acre,  or  a 
httle  more  than  a  ton  for  a  lot  50  feet  by  1 50  feet.  A  birch-tree,  with  some  200,000 
leaves,  was  estimated  to  give  off  700  to  900  pounds  on  a  hot  summer  day,  but 
much  less  on  a  cool  day. 

Water  vapor  also  enters  the  air  from  all  active  volcanoes  (p.  191). 
The  oceans,  however,  are  the  great  evaporating  pans  from  which  most 
water  vapor  comes,  and  but  for  them  the  waters  of  the  land  would  all 
be  dried  up  in  the  course  of  time. 

Water  is  in  constant  circulation  in  the  air.  The  circuit  which  it 
makes  is  somewhat  as  follows:  (i)  It  is  evaporated  from  the  ocean 
(and  all  moist  surfaces) ;  (2)  as  vapor,  it  is  diffused  and  blown  over  the 
land,  where  some  of  it  (3)  is  condensed  and  falls  as  rain  or  snow.  A 
part  of  the  rain  which  falls  on  the  land  returns  directly  to  the  sea 
through  rivers,  a  part  sinks  into  the  ground,  and  another  part  is  evap- 
orated again.  About  half  the  water  vapor  of  the  air  is  below  an 
altitude  of  6,500  feet.  Its  abundance  near  the  bottom  of  the  air 
is  one  reason  why  the  lower  air  is  warmer  than  that  above  (p.  44). 

On  the  average,  30  to  40  inches  of  rain  fall  each  year  on  land ;  that 
is,  enough  to  make  a  layer  30  to  40  inches  in  average  depth  if  spread 
out  over  all  the  land.  The  amount  of  water  evaporated  from  the 
oceans  each  year  is  about  the  same  as  that  which  falls  from  the  air. 
If  precipitation  (rainfall  and  snowfall)  on  the  oceans  is  equal  to  that 
on  the  lands,  square  mile  for  square  mile,  and  if  all  the  water  of  the 
rain  and  snow  came  from  the  oceans  and  was  not  returned  to  them, 
the  oceans  would  be  dried  up  in  3,000  or  4,000  years.  If  an  amount 
of  water  equal  to  all  the  rainfall  of  a  year  were  evaporated  from 
lakes,  they  would  probably  all  be  dried  up  in  less  than  a  year. 


58  CLIMATIC   FACTORS:    MOISTURE 

Rate  of  evaporation.  The  principal  conditions  affecting  the 
rate  of  evaporation  are  (i)  the  amount  of  water  vapor  already  in  the 
air,  (2)  the  temperature  of  the  surface  and  the  air  over  it,  and  (3)  the 
-strength  of  the  wind.  At  a  given  temperature,  the  less  the  water 
vapor  in  the  air,  the  more  rapid  the  evaporation  from  a  water  surface. 
Raising  the  temperature  of  air  from  30°  to  50°  F.  doubles  its  capacity 
to  hold  water  vapor,  and  hence  increases  the  rate  of  evaporation. 
Air  moving  10  miles  an  hour  will  evaporate  four  times  as  much  water 
as  still  air,  other  things  being  equal. 

Effect  of  evaporation  on  temperature.  Evaporation  cools  the 
surface  from  which  it  takes  place.  If  the  hand  be  moistened,  it  feels 
cool  as  the  water  on  it  evaporates,  and  the  faster  the  evaporation, 
the  more  distinct  the  cooling.  Moist  clothing  seems  cooler  in  wind 
than  in  still  air,  even  when  the  temperature  is  the  same,  because 
wind  increases  evaporation.  For  the  same  reason,  a  day  in  summer 
when  the  wind  is  blowing  seems  cooler  than  a  calm  day  when  the 
temperature  is  the  same. 

Evaporation  from  forested  regions  in  moist  tropical  lands  is  so  great  that  the 
temperature  there  is  much  lower  than  would  be  expected  from  the  insolation.  The 
slight  evaporation  from  dry  regions  is  one  reason  why  they  are  so  hot  in  the  sunny 
days  of  summer.  Dry  heat  is  less  uncomfortable  than  damp  heat  because  the 
increased  evaporation  from  the  human  body  in  a  dry  region  reduces  its  temperature. 
The  hot,  dry  air  of  a  furnace  room  causes  far  less  discomfort  than  the  less  hot,  damp 
air  of  a  green-house.  On  the  other  hand,  moist  air  at  0°  F.  seems  much  cooler  than 
dry  air  at  the  same  temperature. 

Sensible  temperature.  The  difference  between  temperature  as 
it  seems  {sensible  temperature)  and  temperature  as  it  is  (shown  by  the 
thermometer)  is  often  great.  Thus,  observations  in  Death  Valley, 
California,  showed  a  maximum  air  temperature  of  122°  on  five  days, 
but  the  sensible  temperatures  ranged  from  73°  to  77°  F.  Yuma, 
Arizona,  with  an  average  temperature  of  92°  in  July,  does  not  seem 
so  hot  as  Savannah,  with  a  temperature  of  82°,  and  but  little  hotter 
than  Boston,  with  a  temperature  of  72°.  This  is  because  the  air  at 
Yuma  is  very  much  drier  than  that  at  Savannah  or  Boston.  Sensible 
temperatures  bear  a  very  important  relation  to  sunstroke  and  heat 
prostration,  both  of  which  are  almost  unknown  in  our  dry  south- 
western states,  but  are  of  frequent  occurrence  along  the  less  hot  but 
more  moist  eastern  coast. 

Saturation.  The  amount  of  water  vapor  in  the  air  varies  greatly 
from  place  to  place,  and  from  time  to  time  at  the  same  place.    When 


HUMIDITY   AND   LIFE  59 

there  is  as  much  water  vapor  in  the  air  as  there  can  be  under  existing 
conditions,  it  is  said  to  be  saturated.  A  cubic  foot  of  air  at  0°  F.  is 
capable  of  containing  ^  grain  of  water  vapor;  at  30°,  about  2  grains; 
at  60°,  5  grains;  at  80°,  11  grains;  and  at  90°,  nearly  15  grains.  Thus 
the  higher  the  temperature  the  greater  the  amount  of  water  vapor 
necessary  for  saturation. 

Humidity 

Absolute  and  relative  humidity.  The  amount  of  moisture 
which  the  air  contains  is  its  absolute  humidity.  The  percentage  of 
moisture  which  air  contains  at  any  temperature,  compared  with 
what  it  might  contain  at  that  temperature,  is  its  relative  humidity. 
If  a  cubic  foot  of  air  at  30°  F.  contains  2  grains  of  water  vapor,  it 
is  saturated,  and  its  relative  humidity  is  100  per  cent.  If  the  tem- 
perature is  raised  to  60°  F.,  its  capacity  for  water  vapor  is  increased 
from  2  grains  to  5  grains,  and  its  relative  humidity  is  then  40  per  cent. 
On  the  other  hand,  if  air  at  80°  F.,  containing  5  grains  of  water  vapor 
(relative  humidity  about  46  per  cent),  were  cooled  to  60°  F.,  the  5 
grains  would  mean  saturation  for  that  temperature.  Air  is  said  to 
be  "dry"  when  its  relative  humidity  is  low,  and  "moist"  when  its 
relative  humidity  is  high.  Thus  5  grains  of  water  vapor  in  air  at  90° 
F.  means  dry  air  (humidity  33),  while  the  same  quantity  of  water 
vapor  in  air  at  60°  F.  means  damp  air.  The  air  over  damp  England 
and  that  over  the  dry  Sahara,  for  example,  may  have  the  same  actual 
amount  of  water  vapor  per  cubic  foot. 

The  average  relative  humidities  in  the  United  States  range  from  80  along  the 
coasts  to  less  than  40  in  some  parts  of  the  southwest.  Areas  where  the  relative 
humidity  is  35  or  less  are  essentially  desert,  and  areas  where  it  is  less  than  50  are 
distinctly  dry.  The  average  relative  humidity  of  air  over  the  land  is  probably 
about  60;  that  over  the  ocean  about  85.  In  that  part  of  the  United  States  where 
ordinary  farming  can  be  carried  on  without  irrigation,  the  relative  humidity  is,  as 
a  rule,  more  than  65. 

Importance  of  relative  humidity.  Corn,  wheat,  and  rye, 
require,  respectively,  about  14,  10,  and  8  inches  of  water  during  their 
growing  seasons.  If  the  total  rainfall  of  a  given  place  is  18  inches  in 
that  time,  any  one  of  the  crops  would  seem  to  have  enough.  But  if 
the  relative  humidity  is  very  low,  evaporation  is  rapid.  In  this  case 
jb  inches  of  rain  may  be  necessary  to  grow  rye. 

Relative  humidity  has  important  effects  on  the  human  body.  Moisture  is 
all  the  time  being  evaporated  from  the  skin  and  lungs.  High  humidity  checks 
evaporation,  and  this  seems  to  be  one  cause  of  certain  diseases  in  moist  tropical 


6o  CLIMATIC   FACTORS:    MOISTURE 

regions.  Low  humidity  increases  evaporation  from  the  body,  and  this  is,  on  the 
whole,  stimulating.  Sudden  changes  from  low  to  high  humidity,  especially  when 
associated  with  sudden  changes  of  temperature,  such  as  occur  when  one  goes  out 
from  a  warm  house  in  winter,  probably  favor  diseases  of  the  breathing  organs  (cold, 
etc.),  so  frequent  at  that  season. 

High  relative  humidity  hastens  the  decay  of  food,  especially  meat;  hence 
many  foods  cannot  be  kept  long  in  warm,  moist  places.  This  is  perhaps  one 
reason  why  little  meat  is  used  in  tropical  countries.  Unprotected  iron  wares  rust 
rapidly  in  damp  air.  The  damp  air  of  the  coast  of  Maine  prevented  the  successful 
development  of  the  sardine  industry,  in  spite  of  a  law  providing  that  the  drying 
should  be  done  only  on  "dry  clear  days,"  until  a  special  method  of  curing  the  fish 
made  it  possible  to  compete  with  the  French  product  dried  out  of  doors.  In  some 
places  meat  is  dried  in  the  air,  giving  the  so-called  "jerked  beef."  Even  "burial" 
of  the  dead  may  be  on  high  platforms  in  regions  where  dry  air  quickly  mummifies 
the  body. 

Extreme  drjoiess  and  the  evaporation  which  goes  with  it  cause  wood  to  shrink, 
warp,  and  crack  to  such  an  extent  that  boxes  which  were  strong  fall  apart.  Goods 
to  be  shipped  far  through  a  very  dry  region  need  special  preparation,  and  even 
railroad  cars  have  to  be  of  steel  to  withstand  the  effect  of  desert  dryness.  Humidity 
is  so  important  in  textile  industries,  as  in  spinning  cotton,  that  the  early  centers 
of  cotton  manufacture  tended  to  develop  in  damp  regions.  In  many  mills,  special 
devices  are  now  used  to  maintain  uniform  humidity. 

Dew  point.  If  saturated  air  (p.  59)  is  cooled,  some  of  its  water 
vapor  is  condensed  (becomes  liquid).  The  temperature  at  which  it 
begins  to  condense  is  the  dew  point.  Air  may  be  brought  to  the  dew 
point  in  various  ways:  (i)  It  may  be  blown  where  the  temperature 
is  lower,  as  to  a  higher  latitude  or  altitude;  (2)  it  may  be  cooled  by 
having  cooler  air  brought  to  it,  as  by  a  cold  wind;  (3)  it  may  be  cooled 
by  radiation,  or  (4)  by  expansion,  as  when  it  rises. 

The  temperature  of  the  dew  point  is  not  fixed,  but  is  influenced 
by  the  amount  of  water  vapor  in  the  air,  as  already  explained  (p,  59). 
If  air  at  80°  F.  contains  5  grains  of  vapor  per  cubic  foot,  its  dew  point 
will  be  reached  when  it  is  cooled  to  60°  F. ;  but  if  the  amount  of  water 
vapor  in  air  at  80°  F.  is  only  2  grains  per  cubic  foot,  the  dew  point 
would  not  be  reached  until  it  had  been  cooled  to  30°  F. 

If  the  temperature  of  condensation  is  above  32°,  the  vapor  con- 
denses into  liquid  water,  which  at  first  takes  the  form  of  droplets, 
such  as  those  of  which  fog  is  made.  If  the  temperature  of  condensa- 
tion is  below  32°,  particles  of  ice  form  as  the  vapor  condenses. 
They  may  be  the  beginnings  of  snowflakes,  or  they  may  be  particles 
of  frost.  The  condensation  of  water  vapor  sets  free  an  amount  of 
heat  equal  to  that  absorbed  in  its  evaporation.  This  heat  checks 
the  cooling,  a  fact  of  importance  where  the  temperature  of  condensa- 


FORMS   OF   CONDENSED   VAPOR  6i 

tion  is  near  32°  F.,  and  where  continued  cooling  would  bring  the 
temperature  to  the  freezing  point. 

Dew  and  frost.  In  the  clear,  still  nights  of  summer  and  autumn, 
the  temperature  of  the  surface  of  the  land,  cooling  by  radiation, 
often  becomes  lower  than  the  dew  point  of  the  air  above.  Moisture 
then  condenses  on  the  surface.  Such  moisture  is  dew  if  the  tempera- 
ture of  condensation  is  above  32°.     The  water  which  condenses  on 


Fig.  2  7.   Fog  over  the  lowlands,  as  seen  from  Mount  Wilson,  California.  (Ellerman.) 

the  outside  of  a  pitcher  of  ice-water  (p.  56)  is  dew,  just  as  much  as 
that  which  forms  on  grass  blades.  Dew  does  not  fall,  but  condenses 
on  the  surface  of  solid  objects.  When  the  temperature  of  the  dew 
point  is  below  32°  F.,  the  moisture  which  condenses  on  solid  objects 
condenses  as  ice  particles,  or  frost,  instead  of  dew. 

Dew  is  more  likely  to  form  on  still  nights  than  on  windy  ones,  because  wind 
tends  to  move  away  air  which  is  approaching  its  dew  point,  supplying  other  air  in 
its  place,  and  the  incoming  air  may  be  warmer  or  drier  than  that  which  moved  on. 
Dew  is  more  likely  to  form  on  clear  nights  than  on  cloudy  ones,  because  radiation 
and  cooling  are  greater  when  there  are  no  clouds.  This  association  of  dew  with 
clear  skies  led  the  ancients  to  beheve  that  dew  came  from  the  stars. 

Fog  and  cloud.  The  condensing  of  water  vapor  in  the  air  into 
droplets  makes /og  (Fig.  27)  if  the  droplets  are  in  the  lower  part  of 


62  CLIMATIC  FACTORS:    MOISTURE 

the  atmosphere  at  a  temperature  above  32°  F.  It  makes  ice  particles, 
or  frost,  if  the  temperature  is  below  32°  F.  Water  droplets  and  ice 
particles  in  large  numbers  make  clouds  if  formed  well  above  the 
bottom  of  the  atmosphere  (Figs.  28-31).  Fog  may  be  said  to  be 
cloud  resting  on  the  surface  of  land  or  water.  The  droplets  of  water 
forming  fog  and  cloud  are  very  small,  many  of  them  not  more  than 
V3000  of  an  inch  in  diameter. 

Fogs  are  formed  in  many  cases  where  the  moist  air  over  warmer  water  (e.g., 
a  warm  ocean  current)  blows  over  a  colder  surface  of  water  or  land.  They  often 
form  in  valleys  at  night  (Fig.  27),  especially  in  autumn,  when  the  night  tempera- 
tures are  much  lower  than  those  of  the  day.  The  cooler  air  settles  in  the  valleys, 
and  the  air  there  is  more  hkely  to  be  brought  to  the  dew  point  than  that  over  the 
uplands.  Fogs  occur  more  frequently  in  large  cities  than  in  the  nearby  country, 
apparently  because  the  large  numbers  of  solid  particles  poured  into  the  air 
in  the  form  of  smoke  favor  condensation.  In  London,  fogs  increased  as  more 
coal  was  burned  until  the  "smoke  nuisance"  was  partly  stopped;  then  the  fogs  de- 
creased. In  other  places,  also,  doing  away  with  smoke  has  nearly  put  an  end  to  fogs. 

Fogs  interfere  with  all  kinds  of  traffic.  They  are  the  most  common  cause  of 
disasters  at  sea,  as  in  the  colUsion  of  the  French  steamship  La  Burgogne  with  an 
iceberg  in  the  North  Atlantic,  as  a  result  of  which  more  than  600  lives  were  lost. 
Coastwise  traffic,  as  in  Nantucket  Sound,  or  traffic  in  river  harbors,  as  at  Philadel- 
phia, is  kept  at  a  standstill  for  days  at  a  time  by  fogs.  Fogs  also  have  caused 
many  railway  accidents. 

In  some  places  where  fogs  are  frequent  and  heavy,  they  may  serve  as  a 
source  of  moisture.  The  distribution  of  the  redwood  tree  in  California  corresponds 
closely  to  the  zone  over  which  fogs  extend  inland.  Along  some  African  rivers  the 
moisture  from  valley  fogs,  always  drifted  one  way  by  the  winds,  causes  heavier 
vegetation  on  one  bank  than  on  the  other.  Attempts  by  men  to  utiUze  the  moisture 
of  fogs  have  never  proved  very  successful. 

Forms  of  clouds.  Clouds  take  many  forms,  (i)  Cumulus  clouds 
are  thick,  with  upper  surfaces  somewhat  dome-shaped,  and  with 
irregular  and  fleecy  projections.  Their  bases  are  nearly  horizontal 
(Fig.  28).  They  are  formed  from  the  water  vapor  in  ascending  con- 
vection currents,  and  their  level  bottoms  seem  to  mark  the  altitude 
at  which  condensation  takes  place  as  the  air  rises.  Their  bottoms 
are  usually  somewhere  from  1,800  to  4,000  feet  above  the  land,  but 
the  tops  may  rise  three  or  four  miles  higher.  They  appear,  especial- 
ly in  clear,  hot  weather,  in  mid-  or  late-forenoon,  after  insolation  has 
established  convection  currents.  They  attain  their  greatest  size 
at  about  the  hour  of  maximum  heat.  As  evening  approaches  they 
commonly  grow  smaller  and  disappear.  (2)  Stratus  clouds  are  hori- 
zontal sheets  of  cloud,  often  not  more  than  1,000  feet  above  the  earth. 
(3)  Nimbus  or  rain  clouds  (Fig.  29)  consist  of  thick  masses  of  dark 


TYPES   OF   CLOUDS 


63 


clouds  without  definite  shape  and  with  ragged  edges,  from  which 
continued  rain  or  snow  generally  falls.  Nimbus  clouds  are  rarely- 
more  than  half  a  mile  above  the  earth's  surface.  (4)  Cirrus  clouds 
are  delicate,  fibrous,  or  feathery  (Fig.  30).     They  are  generally  white, 


Fig.  28. 


Fig.  29. 


Fig.  28. 
Navy.) 

Fig.  29. 
of  Navy.) 

Fig.  30. 

Fig.  31- 
of  Navy.) 


Fig.  30.  Fig.  31. 

Cumulus   clouds.     (Cloud   chart,   Hydrographic   Office,   Dept.   of 

Cumulo-nimbus  clouds.     (Cloud  Chart,  Hydrographic  Office,  Dept. 

Cirrus  clouds.     (Cloud  Chart,  Hydrographic  Office,  Dept.  of  Navy.) 
Cirro-stratus  clouds.     (Cloud  Chart,  Hydrographic  Office,   Dept. 


and  sometimes  arranged  in  belts.  They  are  usually  high,  five  miles 
or  more,  and  thin,  and  probably  always  consist  of  particles  of  snow  or 
ice.  Between  these  types  of  clouds  there  are  many  gradations,  of 
which  perhaps  the  most  interesting  is  the  cirro-stratus  (Fig.  ji),  a 
thin,  veil-like  cloud,  almost  imperceptible,  usually  extending  in  a  -^heet 
over  a  large  part  of  the  sky. 


64  CLIMATIC  FACTORS:    MOISTURE 

In  general,  cirrus  and  cumulus  clouds  are  fair-weather  clouds, 
and  do  not  give  precipitation.  The  latter,  however,  may  grow  into 
the  cumulo-nimbus  or  summer  thunder  cloud  (Fig.  29),  lose  their 
fleecy  whiteness,  and  produce  rain.  Cirro-stratus,  stratus,  and  nim- 
bus clouds  are  more  likely  to  be  foul-weather  clouds. 

Cloudiness  and  sunshine.  The  chief  importance  of  clouds  is 
found  in  their  relation  to  (i)  precipitation  and  (2)  sunshine.  Clouds 
cut  off  sunshine  and  reduce  the  amount  of  insolation;  hence  they 
lower  day-time  temperatures.  Clouds  also  check  radiation,  and 
so  tend  to  keep  night  temperatures  higher.  Cloudy  regions,  there- 
fore, have  less  variable  temperatures  than  clear  ones.  Through  their 
effect  on  temperatures,  clouds  also  affect  humidity  and  evaporation, 
raising  humidity  and  lowering  evaporation.  Hence  cloudy  places 
are  generally  cool  and  damp  and  the  t>T3es  of  vegetation  and  the 
crops  grown  there  are  different  from  those  of  places  in  the  same 
latitude  where  clouds  are  few.  Thus  there  are  few  vineyards  in 
cloudy  regions,  wine  production  being  typical  of  sunny  countries. 

In  general,  great  cloudiness  goes  with  great  relative  humidity. 
Cloudiness  is  somewhat  greater  in  winter  than  in  summer,  greater 
in  higher  latitudes  than  in  low  ones,  and  greater  along  sea-coasts 
than  in  continental  interiors.  The  sunniest  parts  of  the  earth  are  hot 
deserts. 

Precipitation.  The  condensation  of  the  water  vapor  of  the  air 
leads  to  rain,  snow,  or  hail,  if  the  products  of  condensation  fall. 
Whether  precipitation  really  takes  place  after  the  formation  of  clouds, 
depends  on  many  conditions.  To  give  rain  or  snow,  the  particles  of 
water  or  snow  in  the  cloud  must  be  large  enough  to  fall.  Drops  of 
rain  vary  in  diameter  from  Vso  to  ^/s  of  an  inch.  If  they  are  to  reach 
the  ground  they  must  not  pass  through  air  which  is  dry  enough  and 
warm  enough  to  evaporate  them  before  they  reach  the  bottom  of  the 
atmosphere.  In  desert  regions,  water  may  sometimes  be  seen  to  be 
falling  from  a  high  cloud,  when  not  a  drop  reaches  the  ground.  The 
falling  drops  evaporate  as  they  descend. 

Precipitation  and  evaporation.  The  distribution  of  rainfall 
depends,  in  large  measure,  on  the  winds,  and  will  be  considered  later. 
The  amount  of  rain  necessary  for  crops  is  affected  greatly  by  rela- 
tive humidity  and  evaporation.  Thus  two  localities  which  have  the 
same  amount  and  seasonal  distribution  of  rainfall  may  have  very 
different  sorts  of  plants,  because  more  of  the  precipitation  in  one  place 
is  evaporated  quickly. 


EVAPORATION   AND   PLANT  LIFE  65 

In  some  parts  of  western  Texas,  with  a  precipitation  of  22  inches,  there  is 
too  little  moisture  for  crops  unless  they  are  grown  by  "dry-farming"  (p.  329), 
and  the  region  is  given  over  largely  to  grazing.  In  the  valley  of  the  Red  River  in 
Minnesota  and  North  Dakota  the  precipitation  is  a  little  less;  yet  this  is  one  of  the 
most  important  wheat  regions  of  the  world.  The  difference  between  the  two 
regions  is  due  chiefly  to  the  fact  that  evaporation  is  about  2>^  times  as  great  in 
Texas  as  in  the  Red  River  Valley,  because  of  the  higher  temperature  in  the  former 
place. 

In  many  other  locaUties  where  rainfall  is  scanty,  evaporation  is  one  of  the 
most  important  of  all  climatic  factors,  so  far  as  vegetation  is  concerned.  Dry- 
farming  depends  partly  on  the  principle  that  if  evaporation  from  the  soil  is  checked, 
even  scanty  rainfall  (15  inches  yearly)  may  suffice  for  hardy  crops  hke  wheat. 
The  so-called  "hot  winds"  which  sometimes  do  great  damage  to  the  com  crop,  as 
in  Kansas  and  Nebraska,  owe  their  destructiveness  chiefly  to  the  rapid  evaporation 
caused  by  their  warmth  and  dryness.  If  these  winds  were  moist,  their  temperature 
would  not  hurt  the  corn.  Desert  plants  have  peculiar  characteristics  such  as 
fleshy  leaves  and  smooth,  shining  surfaces,  developed  apparently  with  reference  to 
preventing  loss  of  moisture  by  evaporation. 


Questions 

1.  Why  is  the  crop  in  a  grain  field  poor  around  the  base  of  a  tree? 

2.  Where,  in  middle  latitudes,  would  you  expect  the  sensible  temperature  to 
be  highest  in  summer?     In  winter?     The  same  for  tropical  regions. 

3.  Why  is  the  relative  humidity  in  houses  in  winter  diff'erent  from  that  out  of 
doors,  even  where  the  furnace  has  a  supply  pipe  taking  in  outside  air? 

4.  What  is  the  effect  of  the  indoor  relative  humidity  in  winter  on  the  amount 
of  fuel  burned? 

5.  Beds  of  rock  salt  are  found  underground  in  some  places.     What  con- 
clusion may  be  drawn  as  to  the  cUmate  when  the  deposit  was  formed? 

6.  Why  does  fog  in  the  evening  appear  first  close  to  the  ground? 

7.  Why  are  clouds  rarely  formed  above  an  altitude  of  10  miles? 

8.  Why  does  most  of  the  heavy  precipitation  come  from  low  clouds? 

9.  What  is  the  reason  for  the  formation  of  more  dew  on  surfaces  of  stone  or 
metal  than  on  pieces  of  wood  near  by? 

10.  Explain  the  fact  that  the  lower  leaves  or  branches  of  a  plant  may  be 
nipped  by  frost,  when  the  upper  parts  of  the  same  plant  are  unaffected. 

11.  Why  is  frost  less  likely  to  occur  on  cloudy  than  on  clear  nights? 

12.  Why  are  frosts  less  common  after  heavy  rain  than  at  other  times? 

13.  Why  does  a  covering  of  newspapers  or  of  thin  cloth  often  protect  plants 
from  frost? 

14.  Suggest  other  means  by  which  protection  from  frost  might  be  secured  for 
large  fruit  orchards  and  truck  farms. 

15.  At  what  time  of  day  is  relative  humidity  lowest,  on  the  average?    Why? 


CHAPTER  VII 
CLIMATIC   FACTORS:     PRESSURE  AND  WIND 

Pressure 

Importance  of  pressure.  The  downward  pressure  (or  weight) 
of  the  air  is  about  15  pounds  to  the  square  inch  at  sea-level.  The 
pressure  varies  a  little  from  time  to  time  at  any  given  place,  and  is 

rarely  the  same  at  any  two  places  more  than  a 
few  miles  apart.  In  themselves,  variations  of 
pressure  have  little  effect  on  life;  but  the  vari- 
ations have  much  to  do  with  winds  and  other 
elements  of  weather,  and  weather  is  most  impor- 
tant to  life.  Hence  it  is  desirable  to  have  some 
simple  method  of  measuring  and  recording  at- 
mospheric pressures.  The  instrument  by  which 
they  are  measured  is  the  barometer. 

The  barometer.  The  principle  of  the  barometer  is  as 
follows:  A  tube  more  than  30  inches  long,  closed  at  one 
end,  is  filled  with  mercury.  The  open  end  of  the  tube  is 
then  placed  in  a  dish  of  mercury  (Fig.  32).  The  mercury 
in  the  tube  will  sink  until  its  upper  surface  reaches  a  level 
about  30  inches  above  the  level  of  the  mercury  in  the 
dish,  if  the  place  of  the  experiment  is  at  sea-level.  The 
mercury  remains  at  this  height  in  the  tube,  because  the 
pressure  of  the  air  on  the  mercury  in  the  dish  is  enough  to 
balance  the  weight  of  the  mercury  in  the  tube.  Since  the 
normal  pressure  of  the  air  at  sea-level  balances  a  column 
of  mercury  about  30  inches  high,  the  pressure  of  the  air  at 
sea-level  is  said  to  be  30  inches.  If  the  pressure  is  more 
than  30  inches  it  is  said  to  be  high;  if  less  than  30  inches, 
low.  At  sea-level  the  variation  above  and  below  30  inches 
is  rarely  more  than  one  inch. 


Fig.  32.  Diagram 
to  illustrate  the  prin- 
ciple of  the  barom- 
eter. The  pressure 
of  the  air  at  A  main- 
tains the  mercury  at 
B  in  the  tube  when 
there  is  no  air  in  the 
tube  above  B. 

normal   pressure 
about  24  inches 


Pressure  and  altitude.    At  elevations  above 

sea-level   the   pressure   grows    less.     Thus    the 

is   about    28  inches   1,800  feet  above    sea-level, 

at  6,000  feet,  and  about  20  inches  at  10,500  feet, 

66 


WHY   AIR   PRESSURE   VARIES  67 

The  rate  of  decrease  of  pressure  vdih  increasing  height  being 
known,  the  altitude  of  a  place  above  sea-level  may  be  measured  by 
means  of  the  barometer.  A  special  form  of  barometer  has  been  de- 
vised for  this  purpose. 

The  decrease  of  pressure  with  altitude  explains  some  of  the  discomforts, 
such  as  mountain  sickness,  experienced  by  many  mountain  climbers.  After  a 
short  stay  at  relatively  high  altitudes,  these  discomiforts  disappear  in  most 
cases. 

Distribution  of  pressure.  The  pressure  of  the  atmosphere  at 
sea-level  varies  from  point  to  point,  and  from  time  to  time  at  the 
same  point.  Some  of  the  reasons  are:  (i)  The  temperature  of  the 
surface  on  which  the  air  rests  is  unequal,  and  increase  of  temperature 
makes  the  air  lighter.  As  the  temperature  varies,  the  pressure  varies. 
(2)  Water  vapor  in  the  air  makes  the  air  lighter  (p.  56).  The  amount 
of  moisture  in  the  air  is  greater  in  warm  regions  (but  not  in  hot  des- 
erts) than  in  cold  ones,  and  greater  over  moist  surfaces  than  over  dry 
ones.  Since  the  amount  of  moisture  in  the  air  varies  from  time  to 
time,  the  pressure  is  changing  constantly. 

Representation  of  Pressure  on  Maps  and  Charts 
Isobars.  For  convenience  in  the  study  of  pressure  distribution, 
lines  may  be  drawn  on  maps  connecting  points  where  the  atmospheric 
pressure  is  the  same.  Such  equal-pressure  lines  are  isobars.  A 
map  showing  lines  of  equal  pressure  is  known  as  an  isobar ic  map  or 
chart.  An  isobaric  chart  for  the  year  shows  isobars  connecting  points 
having  the  same  average  pressure  throughout  the  year.  There  may 
be  isobaric  charts  for  a  season,  for  a  month,  or  for  shorter  periods. 
The  daily  weather  maps  are  daily  isobaric  charts.  Fig.  33  is  an 
isobaric  chart  for  the  year.  The  figures  on  the  lines  indicate  the 
average  pressure  for  the  year  in  inches. 

In  the  southern  hemisphere,  the  isobar  of  30  inches  encloses  a 
belt  extending  almost  around  the  earth,  being  interrupted  only  near 
Australia.  Every  point  within  the  area  enclosed  by  this  isobar  has 
an  average  atmospheric  pressure  of  more  than  30  inches.  Every 
point  within  the  isobar  of  30.10  inches  has  an  average  annual  pressure 
of  more  than  30.10  inches,  while  every  point  between  the  isobars  of 
30  and  30.10  has  an  average  annual  pressure  of  more  than  30  and 
less  than  30.10  inches,  etc.  Between  the  two  adjacent  isobars  of 
29.90  in  the  equatorial  part  of  the  Atlantic,  the  pressure  is,  on 
the  average,   less  than   29.90,  but  not  so  low  as  29.80.     If  the 


68       CLIMATIC  FACTORS:    PRESSURE  AND   WIND 


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RELATIONS   OF  TEMPERATURE  AND   PRESSURE     69 

pressure  sank  to  the  latter  figure,  there  would  have  been  an  isobar 
of  2Q.8o  inches. 

It  will  be  remembered  that  in  the  case  of  the  isothermal  chart 
allowance  is  made  for  altitude  above  sea-level.  In  the  same  way, 
the  pressures  shown  on  land  on  an  isobaric  chart  are  those  which 
would  exist  if  there  were  no  elevations  above  sea-level.  For  low 
altitudes  the  pressure  decreases  about  .  i  inch  for  each  90  feet  of  rise. 

Courses  of  isobars.  Returning  to  Fig.  t,^,  several  points  are 
seen  readily:  (i)  The  isobars  have  a  general  east-west  course, 
though  many  of  them  are  not  straight;  (2)  on  the  average,  they  show 
greater  pressure  in  low  latitudes  than  in  high  latitudes;  (3)  they  are 
highest  (that  is,  they  show  highest  pressures)  in  the  latitudes  just  out- 
side the  tropics;  (4)  they  are  more  regular  in  the  southern  hemisphere 
than  in  the  northern;  and  (5)  they  are,  on  the  whole,  more  regular 
on  the  sea  than  on  the  land. 

The  isobaric  map  for  January  (Fig.  34)  shows  also  that  a  high- 
pressure  belt  is  very  wide  in  the  northern  hemisphere,  especially  on 
the  land,  which  at  this  season  (winter)  is  cooler  than  the  sea.  This 
fact  suggests  that  high  pressure  goes  with  low  temperature.  In  the 
southern  hemisphere,  January  is  a  summer  month,  and  the  land  is 
warmer  than  the  sea.  If  high  temperature  causes  low  pressure,  the 
pressure  in  the  southern  hemisphere  at  this  time  should  be  less  than 
that  in  the  northern,  and  it  should  be  lower  on  the  land  than  on  the 
sea.  The  map  shows  that  both  these  things  are  true.  This  chart, 
therefore,  seems  to  show  that  high  temperature  reduces  pressure. 

A  study  of  the  isobaric  chart  for  July  (Fig.  35)  leads  to  the  same 
conclusion.  At  that  time  of  year,  the  pressure  in  the  southern  hemi- 
sphere (winter)  should  be  higher,  on  the  average,  than  in  January 
(Fig.  34) ;  especially  should  it  be  higher  on  land,  as  the  map  shows  it 
to  be.  In  the  northern  hemisphere  in  July,  on  the  other  hand,  the 
pressure  should  be  less  than  it  was  in  January,  and  especially  should 
it  be  less  on  land,  which  is  much  warmer  than  it  was  in  winter.  Fig. 
35  shows  both  these  things  to  be  true.  We  have  confidence,  there- 
fore, in  the  conclusion  that  high  temperature  reduces  the  pressure, 
while  low  temperature  increases  it.  The  charts  furnish  other  evi- 
dences in  support  of  the  same  conclusions. 

If  temperature  alone  controlled  pressures,  they  should  be  lowest 
near  the  equator,  where  it  is  warmest,  and  highest  near  the  poles,  where 
it  is  coldest.  Fig,  ^^  shows  that  the  average  annual  pressures  are 
distributed  in  apparent  disregard  of  temperature,  for  the  pressures 


70       CLIMATIC  FACTORS:    PRESSURE  AND  WIND 


ISOBARIC   CHARTS 


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72         CLIMATIC  FACTORS:   PRESSURE  AND   WIND 

are  highest  neither  where  it  is  coldest  nor  where  it  is  warmest.  It 
is  clear,  therefore,  that  neither  temperature  nor  latitude  entirely 
controls  the  distribution  of  pressure. 

Isobars  and  humidity.  We  have  seen  (p.  56)  that  water 
vapor  makes  the  air  lighter.  But  the  isobars  are  not  lowest  over  the 
oceans  in  warm  latitudes,  where  the  air  contains,  on  the  average,  most 
moisture.  We  conclude,  therefore,  that  the  amount  of  moisture  in 
the  air  is  not  the  chief  factor  controlling  the  isobars. 

Inequalities  of  temperature  and  moisture  in  the  air  are  the  only 
factors  thus  far  studied  which  might  affect  the  isobars;  and  since 
they  do  not  explain  the  most  striking  feature  in  the  distribution  of 
atmospheric  pressure,  namely,  the  high  pressures  in  relatively  low 
latitudes,  we  conclude  that  something  besides  temperature  and  mois- 
ture must  be  involved  in  their  explanation.  The  explanation  of  the 
high  pressures  just  outside  the  tropics  is  not  found  on  the  isobaric 
charts,  and  will  not  be  discussed  here. 


Winds 

Importance.  Horizontal  movements  of  air  are  winds.  Winds 
are  important  in  many  ways,  as  in  carrying  away  the  impurities  of 
city  air,  in  transporting  dust  and  sand  (p.  201),  in  furnishing  power 
for  windmills  and  sailing  vessels,  in  increasing  evaporation  (p.  58), 
and  in  distributing  the  moisture  of  the  air  (p.  76).  Winds  also  affect 
human  beings  directly,  for  they  lower  the  sensible  temperature,  and 
are,  as  a  rule,  invigorating,  while  calm  air  (if  warm)  is  enervating. 

Winds  are  produced  by  unequal  pressures  at  the  same  level. 
These  inequalities  are  being  renewed  all  the  time  by  unequal  heating, 
and  in  other  ways ;  hence  winds  always  are  blowing. 

Relation  of  winds  to  the  distribution  of  insolation.  If  the 
air  over  the  whole  earth  were  quiet  at  a  uniform  low  temperature, 
and  if  it  could  then  be  heated  by  the  sun  for  a  time  without  any 
horizontal  movement,  the  effect  would  be  to  raise  its  surface  every- 
where, and  to  raise  it  most  where  it  was  heated  most,  that  is,  in  low 
latitudes  (Fig.  36).  Under  these  conditions  there  would  be  a  baro- 
metric slope  from  low  latitudes  toward  high  latitudes.  Before 
horizontal  movement  began,  there  would  be  no  change  of  pressure 
at  the  bottom  of  the  air,  for  the  same  amount  (mass)  of  air  would 
lie  over  each  place,  as  before  the  heating.  But  if  the  surface  of 
the  air  had  the  form  shown  by  the  dotted  line  in  Fig.  36,  the  upper 


WHY  WINDS   BLOW  73 

air  would  move  as  shown  by  the  arrows.  Since  the  air  in  low  lati- 
tudes is  always  warmer  than  that  in  high  latitudes,  the  upper  air 
should  always  be  moving  from  the  equatorial  zone  toward  the  polar 
zones  in  both  hemispheres.  These  poleward  movements  of  the 
upper  air  lessen  the  pressure  at  the  bottom  of  the  atmosphere  in 
low  latitudes,  because  air  has  moved  away  from  them.  After  air 
has  moved  from  the  equatorial  region  toward  the  poles  (Fig.  36),  there 
is  more  air  over  a  given  spot  in  high  latitudes  than  in  low.  A  baro- 
metric slope  is  thus  established  toward  the  equator  at  the  bottom  of 
the  atmosphere.  Air  then  moves  from  higher  latitudes  to  lower 
latitudes  at  the  bottom  of  the  air  (Fig.  37).     Here,  then,  we  have  the 


90°  0°  90° 

Fig.  36.  The  lower  line  may  be  taken  to  represent  the  surface  of  the  earth; 
the  upper  solid  line,  the  outer  surface  of  the  atmosphere  as  it  would  be  if  the 
temperature  were  everywhere  equal.  The  dotted  line  shows  the  effect  of  heating 
on  the  surface  of  the  air.     Movement  would  result  as  indicated  by  the  arrows. 


90°  0°  90 

Fig.  37.    The  movement  of  air  indicated  in  Fig.  36  would  result  in  further 
movement  as  shown  by  the  lower  arrows  in  this  figure. 

elements  of  a  general  circulation,  a  poleward  movement  in  the  upper 
air,  and  an  equatorward  movement  in  the  lower  air.  The  unequal 
heating  which  generates  these  movements  is  in  operation  all  the  time. 
Effect  of  the  extra-tropical  belts  of  high  pressure.  From  the 
belts  of  high  pressure  just  outside  the  tropics  the  air  flows  to  areas  of 
lower  pressure  on  either  side,  at  the  bottom  of  the  atmosphere,  giving 
rise  to  distinct  wind  zones.  If  the  earth  did  not  rotate,  these  move- 
ments of  air  would  tend  to  follow  meridians.  Rotation,  however, 
turns  the  air  currents  to  the  right  in  the  northern  hemisphere,  and 
to  the  left  in  the  southern.  It  follows  that  the  winds  blowing 
poleward  from  the  high-pressure  belts  are  turned  toward  the  east 
in  both  hemispheres,  and  so  become  westerly  winds  (southwesterly 
in   the  northern  hemisphere,  and  northwesterly   in  the  southern; 


74        CLIMATIC   FACTORS:    PRESSURE  AND   WTXD 


Fig.  38).  The  winds  blowing  from  the  belts  of  high  pressure 
toward  the  equator  become  easterly  icinds  (northeasterly  in  the 
northern  hemisphere,  and  southeasterly  in  the  southern),  and  are 
known  as  trade-winds  (Fig.  38).  The  zone  along  the  equator,  where 
the  northeasterly  and  southeasterly  trades  meet,  and  where  rising 
currents  of  air  are  stronger  than  horizontal  movements,  is  known  as 

the  zone  of  eqtiatorial  calms,  or 
^ 'doldrums. ^^  The  position  of 
this  zone  of  calms  shifts  a  little 
with  the  sun. 

The  westerly  winds  of  mid- 
dle latitudes  and  the  trades  of 
low  latitudes  are  the  prevailing 
winds  {planetary  winds)  at  the 
bottom  of  the  atmosphere. 

Periodic  Winds 
When  air  is  heated  it  ex- 
pands, and  a  given  volume  of 
it  becomes  lighter.  This  results 
in  movements  of  convection 
(Fig.  37).  One  of  the  move- 
ments involved  in  convection  is 
horizontal,  and  horizontal  movement  of  the  air  is  wind.  On  a  cold 
day  in  winter,  with  a  brisk  open  fire,  cold  air  may  be  felt  moving 
along  the  floor  toward  the  fire.  Such  movement  is  analogous  to  wind. 
Unequal  heating  of  the  air  is,  therefore,  a  cause  of  air  movements,  and 
since  the  air  is  being  unequally  heated  all  the  time,  unequal  heating  is 
a  cause  of  constant  atmospheric  movements.  Some  of  the  movements 
are  horizontal,  and  some  vertical;  some  are  in  the  lower  part  of  the 
air,  and  some  in  the  upper. 

The  unequal  heating  of  the  air  is  the  immediate  cause  of  certain 
familiar  winds  and  breezes  which  blow  at  more  or  less  regular  periods 
and  also  interfere  with  the  circulation  indicated  in  Fig.  38. 

Land-  and  sea-breezes.  On  a  sunny  summer  day,  the  land  be- 
comes warmer  than  a  nearby  lake  or  sea  (p.  40).  The  result  is  that 
the  air  over  the  land  is  warmed  and  expanded  more  than  that  over 
the  sea,  and  air  moves  in  from  the  water  to  the  land,  at  the  bottom  of 
the  atmosphere.  This  is  the  sea-breeze  or  lake-breeze.  At  night  the 
land  cools  more  than  the  water,  and  the  air  blows  from  the  land  to 


Generalized    diagram    of 


Fig.  38 
wind   directions   at   the  bottom  of   the 
atmosphere 


SEA-BREEZES   AND   MONSOONS  75 

the  water,  giving  the  land-breeze.  The  sea-breeze  is  strongest  during 
the  summer,  and  in  warm  regions.  In  many  places  it  is  felt  inland 
20  to  30  miles.  It  lowers  the  temperature  over  the  land  to  which  it 
blows,  and  makes  the  conditions  of  life  on  many  tropical  coasts  much 
more  agreeable  than  they  would  be  otherwise.  It  is  partly  because 
of  the  cool,  refreshing  sea-breeze  that  many  people  go  to  the  sea-shore 
during  the  hot  months.  The  effects  of  the  sea-breeze  are  so  bene- 
ficial in  many  places  in  the  tropics  that  the  natives  of  those  regions 
call  the  sea-breeze  the  "doctor."  Along  certain  coasts,  fishermen 
put  to  sea  in  the  early  morning  with  the  land-breeze,  and  return 
toward  night  with  the  sea-breeze. 

Monsoons.  Some  lands  near  the  sea  become  so  warm  in  summer 
that  sea  (from-sea)  winds  blow  throughout  the  hot  season,  while  land 
(from-land)  winds  hold  sway  during  the  winter.  This  is  the  case 
in  India.  Such  winds,  which  change  their  directions  with  the  sea- 
sons, are  monsoon  winds. 

Monsoon  mnds  influenced  greatly  the  development  and  conduct 
of  trade  on  the  Indian  Ocean,  sailing  vessels  timing  their  voyages  so 
as  to  take  advantage  of  them.  The  monsoon  winds  of  India  have 
much  to  do  with  bringing  moisture  from  the  ocean,  thus  influ- 
encing the  rainfall  upon  which  the  crops  to  feed  250,000,000  people 
depend. 

Monsoon  winds,  or  winds  very  much  like  them,  are  not  confined  to 
India.  Winds  blow  from  sea  to  land  in  summer  and  from  land  to  sea 
in  winter  on  the  east  coast  of  Asia.  Spain  affords  another  excellent 
example  of  seasonal  winds. 

Besides  the  winds  mentioned  above,  whose  times  of  blowing  are 
more  or  less  regular,  there  are  winds  which  blow  at  irregular  times, 
and  whose  coming  cannot  be  foretold  long  in  advance.  These  irregu- 
lar winds  are  the  chief  cause  of  the  uncertain  elements  of  the  weather. 
They  will  be  considered  in  the  next  chapter. 

Wind  velocities.  Wind  velocities  are  expressed  usually  in  miles 
per  hour;  thus  the  trade- winds  are  said  to  blow  from  10  to  30  miles  an 
hour.  The  United  States  Weather  Bureau  also  uses  descriptive  terms 
(as  light,  fresh,  brisk)  for  a  regular  scale  of  wind  velocities.  A  wind 
velocity  of  60  mfles  per  hour  causes  a  wind  pressure  of  nearly  10 
pounds  per  square  foot  at  sea-level,  whfle  at  90  miles  an  hour  this 
pressure  is  doubled.  Hence  the  destructive  violence  of  winds  of  high 
velocity.  The  greatest  velocities,  rising  to  100  or  more  miles  per 
hour,  always  are  associated  with  irregular  winds. 


76        CLIMATIC   FACTORS:    PRESSURE  AND   WIND 

The  average  velocity  of  winds  is  greater  over  the  sea  than  over  the  land, 
because  moving  air  is  checked  on  land  by  friction  with  the  uneven  surface.  It  is 
greater  in  tlie  upper  air  than  in  the  lower,  for  the  same  reason.  But  the  force  of 
the  wind  at  high  altitudes  is  less  than  for  the  same  velocities  at  sea-level,  owing 
to  the  less  density  of  the  air  above. 

Winds  and  Rainfall 
Importance  of  rainfall.  Perhaps  the  greatest  service  of  the 
wind  is  in  carrying  moisture  from  the  places  where  it  is  evaporated 
to  the  places  where  it  is  precipitated.  Rainfall  is  of  great  importance 
to  all  plants  and  animals  which  live  on  the  land.  Human  activities, 
too,  are  much  affected  by  rainfall,  for  no  arid  region  supports  a  dense 
population,  and  no  agricultural  country,  aside  from  small  irrigated 
areas,  can  be  prosperous  if  the  rainfall  is  unreliable. 

Less  than  one-thirtieth  of  the  people  of  the  United  States  live  in  the  third  of 
the  country  where  the  rainfall  is  less  than  20  inches  per  year.  Soil  is  not  productive 
unless  adequately  watered,  even  though  it  be  rich  in  the  elements  necessary  for 
plant  food. 

Twenty  inches  of  rain  per  year  usually  is  considered  to  be  the 
minimum  for  general  agricultural  purposes,  but  something  depends 
on  (i)  temperature,  (2)  the  soil,  and  very  much  on  (3)  the  time  of 
year  when  the  rain  falls  and  (4)  the  rate  of  evaporation,  as  determined 
by  temperature,  soil,  and  wind  (pp.  59,  65).  The  warmer  and  drier 
the  climate,  the  more  the  water  needed  for  crops.  A  very  porous 
soil  loses  its  moisture  more  quickly  than  a  more  compact  one,  and 
so  needs  more  rain  for  crops.  The  total  amount  of  rain  necessary  for 
agriculture  is  less  if  it  falls  when  the  growing  crops  need  it  most. 

Rain  and  snow  are  important  not  only  as  a  source  of  water  for  soil,  but  as  a 
source  of  supply  for  streams  and  wells.  A  mantle  of  snow  also  prevents  great 
changes  in  the  temperature  of  the  soil  beneath,  and  in  this  way  protects  many 
plants.  So  important  is  this  effect  that  in  some  regions  a  heavy  snow  generally 
means  good  yields  of  fall-sown  crops  tlie  next  year.  Snow  hampers  some  kinds 
of  transportation  and  favors  others.  In  lumbering,  for  example,  snow  makes 
the  hauling  of  logs  easier.  Rapidly  melting  snow  and  heavy  rainfall  on  frozen 
ground  cause  destructive  floods.  Heavy  rain  in  a  city  is  beneficial  in  flushing 
and  cleaning  the  streets  and  in  washing  impurities  out  of  the  air.  On  the  other 
hand,  it  may  flood  cellars  and  basements,  doing  great  damage.  Both  rain  and  snow 
hinder  the  circulation  of  dust  and  bacteria,  thus  further  contributing  to  health. 

The  precipitation  of  any  given  region  depends  largely  on  (1)  what 
winds  affect  it,  (2)  the  topography  of  the  surface  over  which  the 
winds  blow  before  reaching  it,  and  (3)  the  topographic  situation  and 
relations  of  the  place  itself. 


WINDS  DISTRIBUTE  RAIN  77 

Rainfall  in  the  zones  of  the  trade-winds.  In  the  trade-wind  zones, 
the  vands  blow  from  higher  to  lower  latitudes,  and  therefore,  on  the 
average,  from  cooler  to  warmer  places.  As  the  air  is  warmed,  it 
can  hold  more  moisture.  So  long  as  the  trades  blow  over  the  sea  or 
low  land,  they  take  moisture,  but  do  not  drop  what  they  have.  It 
follows  that  on  the  sea,  and  on  comparatively  low  lands,  like  the 
Sahara  and  parts  of  Australia,  the  trade- winds  are  "dry."  If,  how- 
ever, the  air  of  the  trades  is  forced  up  over  mountains,  it  is  cooled, 
and  some  of  its  moisture  rnay  be  precipitated.  The  windward  sides  of 
high  mountains  in  the  trade-wind  zone  have  heavy  rainfall.  An  illustra- 
tion is  afforded  by  the  east  side  of  the  Andes  Mountains  in  the  trade- 
wind  zone  (Fig.  39) .  Even  in  the  midst  of  the  Sahara  and  of  Australia, 
some  rainfall  is  caused  by  high  hills  and  mountains  which  stand  in 
the  path  of  the  trade- winds. 

After  the  air  of  the  trades  passes  over  a  mountain  range,  it  de- 
scends and  is  warmed  both  by  contact  with  the  warm  surface  and 
by  compression.  It  accordingly  takes  up  moisture.  The  leeward  sides 
of  mountains  in  the  trade-wind  zones  are  therefore  regions  of  little  pre- 
cipitation. The  west  slope  of  the  Andes  Mountains  in  the  zone  of 
the  trades  furnishes  an  example  in  the  coastal  desert  of  Peru. 

Rainfall  in  the  zones  of  the  prevailing  westerlies.  The  wester- 
ly winds  are,  on  the  whole,  blowing  from  lower  to  higher  latitudes,  and 
so  are  being  cooled  gradually.  They  may,  therefore,  yield  some 
moisture  even  at  sea-level  or  on  low  land,  and  especially  on  land  in  the 
winter  .season.  The  heat  of  the  land  in  summer  often  prevents 
condensation  and  precipitation  of  the  moisture  in  the  westerly  winds 
until  the  air  has  moved  far  to  poleward.  But  when  such  winds  cross 
mountains,  they  yield  moisture  to  the  windward  slopes  and  sum- 
mits, and  become  dry  on  the  leeward  slopes  (Fig.  39). 

From  these  principles  we  may  understand  the  rainfall  of  the 
United  States,  so  far  as  it  depends  on  planetary  winds.  The  pre- 
vaiUng  wdnds  for  most  of  the  country  are  from  the  southwest.  Com- 
ing to  the  land  from  the  Pacific  Ocean,  these  winds  find  the  land 
cooler  than  the  ocean  in  winter,  and  warmer  in  summer.  In  winter 
they  yield  moisture,  even  at  low  levels.  This  gives  the  low  lands  of 
California  their  wet  season.  As  the  winds  blow  across  the  mountains 
back  from  the  coast,  they  yield  more  moisture,  so  that  all  the  area 
west  of  the  top  of  the  first  high  ranges,  the  Sierras  at  the  south  and 
the  Cascades  at  the  north,  is  supplied  with  rain  and  snow  in  the 
winter  season.    As  the  winds  blow  beyond  the  Sierra  Nevada  and 


78        CLIMATIC  FACTORS:   PRESSURE  AND  WIND 


RAINFALL  OF   THE  UNITED   STATES  79 

Cascade  mountains,  the  air  descends  and  becomes  warmer,  and 
therefore  dry.  East  of  these  mountains  lie  the  arid  and  semi-arid 
lands  of  the  Great  Basin  and  of  eastern  Oregon  and  Washington. 

When  the  westerly  winds  from  the  Pacific  reach  the  higher  parts 
of  the  Rocky  Mountains,  which  are  higher  in  many  places  than  the 
mountains  farther  west,  they  again  yield  some  moisture.  But  farther 
east,  all  the  way  to  the  Atlantic,  these  winds  are  dry,  for  they  cross 
no  more  high  mountains,  and  they  do  not  generally  go  far  enough  north 
to  reach  a  temperature  as  low  as  that  of  the  mountains  they  have 
passed.  For  some  distance  east  of  the  mountains  the  rainfall  is  slight ; 
but  east  of  central  Kansas  and  Nebraska  the  lands  are  well  supplied 
with  moisture  (Fig.  59).  It  is  therefore  clear  that  something  besides 
the  westerly  winds  brings  rainfall  to  this  region.  This  agent  is 
the  irregular  cyclonic  wind,  to  be  studied  in  the  next  chapter. 

The  winds  which  blow  from  the  Pacific  to  the  continent  in  sum- 
mer have  a  different  effect  upon  rainfall.  At  this  season,  they  find 
a  temperature  on  the  coastal  lowlands  higher  than  their  own.  They 
are  therefore  "dry"  in  this  region,  and  give  to  much  of  California  its 
dry  season.  Blowing  inland,  these  winds  reach  mountains  so  high 
that  the  temperature  is  low  enough  to  cause  condensation  and  pre- 
cipitation, even  while  the  low  lands  to  the  west  are  dry.  In  Wash- 
ington, the  mountains  near  the  coast  are  high  enough  to  cause  pre- 
cipitation even  in  summer.  In  Alaska,  where  some  of  the  mountains 
always  are  covered  with  snow,  precipitation  is  heavy  in  summer,  and 
at  high  altitudes  much  of  it  falls  as  snow. 

Monsoon  winds  may  yield  much  moisture.  In  general,  they 
blow  toward  warmer  regions,  and  so  should  be  dry ;  but  they  may  be 
forced  up  over  high  mountains,  and  precipitation  follows.  The 
heaviest  rainfall  on  record,  on  the  southern  slopes  of  the  Himalayas, 
is  due  to  moonson  wands.  As  in  the  case  of  the  planetary  winds,  it  is 
the  windward  sides  of  the  mountains  which  receive  the  hea\y  precipi- 
tation from  the  monsoons.  It  is  clear,  therefore,  that  the  windward 
sides  of  high  mountains  are  places  of  heavy  rainfall  and  snowfall. 

Variation  in  rainfall.  Some  places  which  w^ere  once  moist  are 
now  dry,  as  shown,  for  example,  by  petrified  forests  in  the  desert  of 
southwestern  United  States.  It  is  believed  that  a  similar  change  in 
the  past  has  made  large  areas  of  central  Asia,  formerly  inhabited,  too 
dry  to  support  more  than  the  scantiest  population.  In  most  places, 
the  rainfall  of  corresponding  months  or  seasons  is  rarely  the  same 
from   year   to   year.    These   temporary   variations   are   important 


8o        CLIMATIC  FACTORS:    PRESSURE  AND   WIND 

factors  (i)  in  floods,  which  in  some  cases  cause  great  damage  to  prop- 
erty and  heavy  loss  of  life  (p.  237),  and  (2)  in  droughts,  which  fre- 
quently result  in  even  greater  loss  through  damage  to  crops,  and  in 
some  countries,  as  India  and  China,  through  deaths  from  famine. 
Australia  has  more  than  once  been  crippled  by  long-continued, 
severe  droughts.  In  the  United  States,  with  other  conditions  equal, 
the  yield  of  corn  depends  directly  on  the  amount  of  rain  falling  in 
June  and  July.  When  the  amount  is  small,  the  crop  is  short.  Other 
crops  show  similar  close  relations  to  rainfall.  The  importance  of 
good  crops  to  the  prosperity  of  the  country  indicates  that  relative 
reliability  of  rainfall  is  a  great  national  asset. 


Questions 

1.  What  effect  do  high  altitudes  have  on  the  power  of  a  steam  engine? 

2.  Explain  fully  the  effects  on  men  (i)  of  a  brisk  wind,  and  (2)  of  calm  air, 
in  summer,  in  Louisiana.     The  same  for  winter. 

3.  Why  are  the  westerly  winds  and  trade-winds  appropriately  called  planetary 
winds? 

4.  On  which  side  of  Lake  Michigan  is  the  lake-breeze  stronger  in  summer? 
Why? 

5.  At  what  time  of  year  would  seasonal  winds  from  Lake  Michigan  be  most 
felt  in  Chicago? 

6.  How  much  force  is  exerted  on  the  side  of  a  house  60  feet  long  by  25  feet 
high,  when  a  wind  is  blowing  90  miles  an  hour? 

7.  How  do  seasonal  (ocean-continent)  winds  affect  the  temperature  of  the 
east  coast  of  North  America  in  summer?  In  winter?  How  do  they  affect  the 
west  coast  at  the  two  seasons? 

8.  In  general,  are  winds  stronger  in  California  in  winter  or  summer?     Why? 

9.  Why  are  the  most  desirable  residential  quarters  of  many  manufacturing 
centers  in  the  United  States  located  to  the  west  and  northwest  of  the  city? 

10.  In  what  portions  of  the  world  would  power  from  the  wind  be  most  reliable? 
In  what  portions  of  the  land  areas?  Why?  Where  is  it  most  likely  to  be  utilized 
by  man? 


CHAPTER   VIII 
STORMS  AND  WEATHER   FORECASTING 

Weather  Maps 

Temperature,  wind,  rainfall  (or  snowfall),  and  cloudiness  are  the 
important  elements  in  the  weather  of  any  place  for  any  given  time. 
As  these  elements  are  combined  in  different  ways  from  day  to  day,  the 
weather  varies.  Weather  changes  are  important  in  so  many  ways  that 
it  is  desirable,  if  possible,  to  know  about  them  before  they  come.  Thus 
winds  of  great  velocity  are  dangerous  to  shipping  at  sea,  and  vessels, 
if  warned  of  their  coming,  may  remain  in  port.  A  freezing  temperature 
in  spring  or  autumn  may  cause  losses  amounting  to  hundreds  of  thou- 
sands, or  even  millions  of  dollars;  but  if  due  warning  is  given,  it  is 
possible  in  some  cases  to  protect  the  crops  which  would  be  injured. 
In  these  ways  and  many  more,  weather  changes  and  weather  forecast- 
ing affect  everyday  life. 

Since  weather  changes  are  associated  directly  with  irregular  winds 
(pp.  85,  90),  and  these  in  turn  depend  on  pressure,  it  is  evident  that 
weather  forecasting  must  depend  largely  on  a  study  of  pressure  con- 
ditions. Changes  of  pressure  from  day  to  day  have  much  more  to  do 
with  weather  changes  than  anything  else  has. 

Isobaric  lines  (p.  67)  and  isothermal  lines  (p.  45)  may  be  put  on 
the  same  map,  which  may  show  also  where  the  sun  is  shining,  where 
it  is  cloudy,  where  it  is  raining,  snowing,  etc.  Such  a  map  is  a  weather 
map,  and  may  be  made  for  any  region,  to  show  the  weather  at  any 
given  time.  Thus  Fig.  40  is  a  weather  map  of  the  United  States  for 
January  g,  191 1.  Like  all  weather  maps,  it  shows  (i)  isobars  (full 
lines);  (2)  the  direction  of  the  winds  (shown  by  arrows);  (3)  the 
degree  of  cloudiness;  (4)  areas  of  precipitation;  and  (5)  isotherms 
(broken  lines). 

Weather  maps  for  the  United  States  are  made  by  the  Weather 
Bureau,  a  branch  of  the  Federal  Department  of  Agriculture.  They 
are  prepared  in  the  chief  cities,  where  telegrams  are  received  twice 
daily  from  numerous  Weather  Bureau  stations  in  different  parts  of 

81 


82 


STORMS  AND   WEATHER   FORECASTING 


INTERPRETATION  OF   WEATHER   MAPS 


83 


the  country,  teUing  the  pressure,  temperature,  direction  and  velocity 
of  the  wind,  cloudiness,  and  rainfall  at  the  station  whence  the  tele- 
gram is  sent. 

Explanation  of  the  Map 

(i)  Isobars.  The  isobars  of  the  map  (Fig.  40)  show  a  range  of 
pressure  from  30.4  inches  in  the  area  centering  in  the  Mississippi 
Valley,  to  29.4  in  Maine,  and  29.2  in  Washington.  The  pressure 
is  more  than  30  inches  in  the  central  part  of  the  country,  and  less 
than  30  inches  on  both  the  Atlantic  and  Pacific  coasts. 

The  isobar  of  30.4  in  the  central  part  of  the  United  States  is  a 
closed  line.  The  center  of  this  high-pressure  area  is  marked  ''high" 
(p.  66).  West  and  east 
of  the  high  the  pressure 
decreases  steadily  toward 
the  coasts,  where  there 
are  centers  of  low  pres- 
sure, marked  "low" 
(p.  66).  The  minimum 
pressure  in  the  low  near 
the  Pacific  coast,  29.2, 
.is  less  than  in  that  over 
Maine,  29.4.  Atmospheric 
pressures  generally  are 
unequal  in  different  parts 
of  the  country.  Hence 
most  weather  maps  show 
both  lows  and  highs,  or  at 
least  one  of  each. 

(2)  Winds.    Wherever 
barometric  pressures  are 

unequal,  winds  are  the  result.  The  arrows  on  a  weather  map  show 
the  direction  of  the  winds.  On  January  9,  191 1  (Fig.  40),  -vvinds 
were  blowing  away  from  the  high  and  toward  the  lows.  The  move- 
ments of  air  out  from  an  area  of  high  pressure  constitute  an  anticy- 
clone, and  the  movements  in  toward  an  area  of  low  pressure  con-  \ 
stitute  a  cyclone.  A  cyclone  is  one  type  of  storm.  The  winds  in  a 
cyclone  are  not  always  strong — rarely  strong  enough  to  be  destruct' 
ive.  The  violent  wind-storms  which  are  popularly  called  cyclones 
should  be  called  tornadoes. 


Fig.  41.  Diagrams  to  show  the  circulation 
of  air  about  a  low,  L,  and  a  high,  H,  in  the 
northern  hemisphere  (N)  and  the  southern  hemi- 
sphere (S). 


84 


STORMS  AND   WEATHER  FORECASTING 


Winds  do  not  blow  straight  out  from  the  anticyclonic  centers,  nor 
straight  in  toward  the  cyclonic  centers.  They  may  start  straight  out 
from  the  center  of  each  high,  but  in  the  northern  hemisphere  they  are 
turned  (deflected)  toward  the  right  (right-hand  half  of  Fig.  41,  N). 
Similarly,  the  winds  which  blow  toward  the  cyclonic  centers  do  not 
blow  straight  toward  them,  but  are  deflected  a  little  to  the  right  in  the 
northern  hemisphere  (Fig.  40,  and  Fig.  41,  N).  In  the  southern 
hemisphere,  the  winds  are  turned  to  the  left  instead  of  to  the  right 
(Fig.  41,  S). 

The  weather  map  tells  nothing  directly  about  actual  wind  veloci- 
ties. This  information  appears  in  a  table  printed  on  the  margin. 
But  the  strength  of  the  winds  at  various  points  may  be  inferred  from 
the  map.  In  general,  the  winds  are  strong  where  isobars  are 
crowded. 

As  air  moves  in  toward  the  center  of  a  cyclone,  it  also  moves 
spirally  up  (Fig.  42).     The  outflow  above  is  chiefly  to  the  eastward. 


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Fig.  42.  Diagram  illustrating  the  general  movement  of  air  currents  in  a 
cyclone  of  middle  latitudes.  The  upper  air  moves  mainly  toward  the  east,  in 
the  direction  of  the  prevailing  winds. 

the  direction  toward  which  the  prevailing  winds  of  middle  latitudes 
blow.  This  upward  movement  has  an  important  effect  on  precipita- 
tion (p.  85). 

(3)  Cloudiness  and  precipitation.  An  open  circle  on  the  shaft 
of  an  arrow  (Fig.  40)  indicates  clear  skies,  a  half-blackened  circle  (as 
in  Wyoming)  shows  that  the  sky  is  partly  cloudy,  while  a  black  circle 
(as  in  Montana)  indicates  general  cloudiness.  An  R  on  the  shaft 
of  an  arrow  (as  in  California)  indicates  rain,  and  an  S  in  the  circle 
on  the  shaft  of  an  arrow  (as  in  New  York)  shows  that  snow  is  falling. 
Amounts  of  precipitation  are  given  in  the  printed  table  with  the  other 
data  for  each  station. 

(4)  Temperature.  As  indicated  above,  the  broken  lines  of  a 
weather  map  are  isotherms.  The  isotherms  of  Fig.  40,  and  of  the 
weather  maps  which  follow,  show  two  distinct  features:    (i)  they 


WEATHER  OF   CYCLONES   AND   ANTICYCLONES     85 

have  little  relation  to  parallels,  and  (2)  all  of  them  bend  northward 
where  the  pressure  is  low,  and  southward  where  the  pressure  is  high. 
These  features  are  less  pronounced  on  maps  showing  storms  of  less 
intensity. 

Cyclones  and  Anticyclones 

Characteristics  of  highs  and  lows.  Highs  and  lows  are  some- 
times much  more  pronounced  than  those  shown  in  Fig.  40.  In 
the  low  of  Fig.  43  the  pressure  ranges  from  29  at  the  center,  to  30.1 
in  the  East,  and  to  30.5  in  the  West.  So  great  a  range  of  pressure 
within  the  United  States  is  uncommon.  The  isobars  are  closer 
together  in  this  figure  than  in  Fig.  40,  and  therefore  indicate  stronger 
winds.     Cloudy  skies  prevail  in  the  southeastern  part  of  the  cyclone. 

Highs  as  well  as  lows  may  have  great  area.  Fig.  44  shows  a  high, 
or  anticyclone,  more  than  2,000  miles  across,  with  a  great  range  of 
pressure.  The  isotherms  of  this  chart,  like  those  of  the  preceding, 
stand  in  very  definite  relations  to  the  isobars.  Denver,  in  the  anti- 
cyclone, is  about  30°  colder  than  the  southern  part  of  Maine,  which 
is  3°  farther  north,  but  on  the  western  border  of  a  cyclone. 

Near  centers  of  low  pressure,  rain  or  snow  falls  in  many  cases, 
while  around  centers  of  high  pressure  there  is,  as  a  rule,  no  precipita- 
tion. The  chief  reason  for  rain  or  snow  about  a  low  is  that  the 
inflowing,  rising  air  expands  and  is  cooled  (p.  60),  and  so  gives  up 
some  of  its  moisture.  In  the  northern  hemisphere,  southerly  winds 
to  the  southeast  of  storm  centers  are,  in  general,  blowing  from  warmer 
to  cooler  places,  and  this  may  result  in  rain  or  snow.  The  prevailing 
winds  which  control  the  outflow  in  the  upper  part  of  a  cyclone  (Fig. 
42)  tend  to  carry  the  rainfall  to  the  east  of  its  center. 

The  circulation  of  winds  around  cyclonic  areas  is  the  real  factor 
in  drawing  moist  air  northward  from  the  Gulf  of  Mexico,  and  in 
giving  abundant  rainfall  east  of  the  Mississippi  River. 

In  an  anticyclone  there  is  a  descending  spiral  movement  of  air. 
The  descending  air  comes  from  an  altitude  where  the  air  is  colder  than 
that  at  the  bottom  of  the  atmosphere,  and  hence  brings  a  low  temper- 
ature. Winds  from  anticyclones  generally  bring  clear  weather,  but 
cold  air  moving  down  and  out  from  an  anticyclone  may  mingle  with 
warm  air  about  it,  so  as  to  cause  some  of  the  moisture  of  the  latter 
to  condense,  giving  rise  to  clouds,  or  even  to  precipitation. 

Movements  of  cyclones  and  anticyclones.  Highs  and  lows  do 
not  remain  in  the  same  place  from  day  to  day.    This  is  shown  by 


86 


STORMS  AND  WEATHER  FORECASTING 


Fig.  43.    Weather  map  for  January  16,  1901,  showing  a  very  pronounced  low. 


Fig.  44.    Weather  map  for  December  9,  1898,  showing  a  high  of  great  size. 


MOVEMENT  OF   STORMS 


87 


Figs.  45-47,  which  are  the  weather  maps  of  three  successive  days.     In 
these  figures  areas  of  precipitation  are  shown  by  shading. 

In  Fig.  45  there  is  (i)  a  low  along  the  Atlantic  coast;  (2)  a  high 
central  over  Iowa;  (3)  a  feeble  low  north  of  Montana;  and  (4)  a  high 
in  Oregon.  The  map  of  the  succeeding  day  (Fig.  46)  shows  (i)  that 
the  low  of  the  Atlantic  coast  has  disappeared  (moved  to  the  east) ; 
(2)  that  the  high  of  the  interior  has  moved  to  West  Virginia;  (3)  that 
the  low  which  was  north  of  Montana  has  moved  to  Dakota;  while  (4) 
the  high  of  the  Oregon  coast  remains  about  where  it  was.  The  map 
of  the  next  day  (Fig.  47)  shows  (i)  that  the  high  of  the  Virginias  has 


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85° 

80°                 75°                70° 

Fig.  45.  Weather  map  for  September  24,  1903.  .The  shading  on  this  and 
succeeding  maps  indicates  areas  of  precipitation  during  the  preceding  24  hours. 

moved  on,  but  not  so  far  as  on  the  preceding  day,  (2)  that  the  low 
which  was  over  North  Dakota  is  now  north  of  Lake  Superior;  (3) 
that  the  high  of  Oregon  has  moved  east  to  Idaho  and  Montana;  and 
(4)  that  a  weak  low  has  developed  in  Oklahoma. 

The  rate  of  progress  of  a  storm  is  not  the  same  as  the  velocity  of 
its  winds.  The  velocity  of  the  wind  depends  on  the  differences  in  pres- 
sure. A  weak  cyclone,  that  is,  one  in  which  differences  of  pressure  are 
not  great,  gives  rise  to  weak  winds,  even  though  the  center  of  the 
storm  moves  rapidly.     A  strong  cyclone,  that  is,  one  in  which  the 


88 


STORMS  AND  WEATHER  FORECASTING 


125°  120°  115°       110°        105°       100°        95°         90°        85' 


75°  70"         65° 


115°  110' 


Fig.  46.    Weather  map  for  September  25,  1903. 


Fig.  47.    Weather  map  for  September  26,  1903. 


PATHS  OF   STORMS 


89 


differences  of  pressure  are  great,  gives  rise  to  strong  winds,  even 
though  the  cyclone  itself  may  move  forward  slowly. 

The  rate  at  which  cyclones  move  varies  with  the  season,  the 
average  being  about  37  miles  per  hour  in  winter  and  22  in  summer. 
Storms  may  move  at  twice  these  rates,  however,  or  at  less  than  half 
their  usual  speed. 

The  course  of  a  cyclone  may  be  shown  on  a  single  map,  as  in 
Fig.  40.  The  row  of  arrows  shows  that  the  low  of  Maine  has  moved 
from  western  Canada.     The  mean  tracks  of  cyclones  and  anticyclones 


Fig.  48.      Chart  showing  the  mean  tracks  of  cyclones  (light  lines)    and  anticy- 
clones (heavy  lines),  and  their  average  daily  movement  (broken  lines). 


for  the  United  States  are  shown  in  Fig.  48.  The  broken  lines  on  this 
map,  marked  i  day,  2  days,  3  days,  and  4  days,  show  the  average 
daily  progress  of  storms  which  come  from  the  northwest. 

Some  anticyclones  enter  the  United  States  from  the  Pacific,  while 
others  start  north  and  northwest  of  Montana,  or,  at  any  rate,  are  first 
reported  from  there.  Cyclones  start  in  various  places.  Many  of 
them  appear  first  near  the  places  where  anticyclones  start,  but  others 
appear  first  in  Colorado,  the  Great  Basin,  Texas,  and  elsewhere. 

The  passage  of  a  cyclone  or  anticyclone  involves  changes  in  the 
direction  of  the  wind,  and  usually  also  changes  of  temperature, 


go  STORMS   AND   WEATHER   FORECASTING 

humidity,  and  cloudiness.  Thus  in  Fig.  46  the  wind  at  St.  Paul  is 
southeasterly,  though  this  city  is  in  the  zone  of  westerly  winds.  The 
next  day,  after  the  storm  center  has  moved  forward  to  a  position 
northeast  of  St.  Paul  (Fig.  47),  the  wind  is  northwesterly.  An  east 
wind  is.  often  the  first  sign  of  an  approaching  cyclone;  and  since 
many  cyclones  bring  rain,  an  east  wind  generally  is  taken  as  a  sign 
of  approaching  rain  throughout  much  of  the  United  States. 

Cyclones  are,  on  the  whole,  more  frequent  and  better  developed 
in  winter  than  in  summer.  They  do  not  affect  the  air  to  great  heights. 
Even  when  the  great  whirl  or  eddy  is  2,000  miles  across,  its  height 
(depth)  is  rarely  more  than  4  or  5  miles.  The  origin  of  the  cyclones 
and  anticyclones  of  middle  latitudes  is  not  well  understood. 

Winds  and  temperatures  incidental  to  cyclones  and  anti- 
cyclones. During  the  passage  of  a  cyclone,  the  air  to  the  southeast 
of  the  storm  center  is  drawn  from  warmer  (lower)  to  cooler  (higher) 
latitudes.  In  midsummer  this  often  gives  rise  to  a  hot  wave,  though 
not  all  hot  waves  are  associated  closely  with  cyclones.  Similar  winds 
are  known  as  the  sirocco  in  the  western  Mediterranean  region,  and  by 
other  names  elsewhere.  In  eastern  United  States,  numerous  sun- 
strokes and  deaths  from  heat  prostration  accompany  some  hot  waves 
in  their  progress  across  the  country. 

Air  to  the  northwest  of  a  cyclone  moves  from  cooler  (higher)  to 
warmer  (lower)  latitudes.  In  winter,  this  may  give  rise  to  cold 
waves.  These  cold  winds  are  known  as  northers  in  the  southern  part 
of  the  United  States,  and  sometimes  as  blizzards  in  the  northern 
part,  though  this  name  usually  implies  heavy  snowfall  and  high  wind, 
as  well  as  low  temperature. 

When  warm,  moist  air  is  forced  up  over  mountains,  it  precipitates 
some  of  its  moisture  (p.  77).  The  precipitation  sets  free  heat,  so 
that  the  rising  air  is  cooled  much  less  than  it  would  be  otherwise. 
Beyond  the  crest  of  the  mountains  it  descends,  and  is  warmed  in  the 
process.  It  is  warmed  much  more  (often  twice  as  much)  in  the 
descent  than  it  was  cooled  in  the  ascent.  It  may,  therefore,  descend 
as  a  hot  win'd.  Such  winds  are  known  as  chinook  winds  in  the  United 
States,  especially  just  east  of  the  P.ocky  Mountains. 

The  chinook  winds  temper  the  rigorous  winters  of  certain  parts  of  the  north- 
western states  and  the  Canadian  provinces  east  of  the  mountains.  They  fre- 
quently evaporate  a  foot  or  more  of  snow  in  a  few  hours.  For  this  reason  they  are 
sometimes  called  "snow-eaters."  These  winds  make  winter  grazing  possible  over 
large  areas  which  otherwise  would  be  covered  heavily  with  snow.     Chinook  winds 


DESTRUCTIVE  TROPICAL   STORMS 


91 


sometimes  develop  with  great  suddenness.     In  some  cases  the  temperature  has 
been  known  to  rise  80°  in  sis  or  eight  hours  under  their  influence. 

The  chinook  winds  of  summer  are  sometimes  so  hot  and  drying  as  to  wither 
vegetation,  and  occasionally  to  destroy  crops. 

Tropical  cyclones.  Cyclones  sometimes  start  in  tropical  regions, 
and  follow  courses  very  different  from  those  of  the  cyclones  of  middle 
latitudes.     Most  of  the  cyclones  of  this  class  which  reach  North. 


Fig.  49.     Course   of   West   Indian   storms   for  August-October,   1878-190O; 
The  heavy  line  indicates  the  mean  track. 


America  originate  in  or  near  the  West  Indies,  and  they  are  most  com- 
mon in  late  summer  and  early  autumn.  They  follow  a  northwesterly 
course  until  the  latitude  of  Florida  is  reached.  Here  they  commonly 
turn  to  the  northward,  and  later  to  the  northeastward,  following  the 
Atlantic  coast.  The  heavy  line  of  Fig.  49  shows  the  average  path  of 
tropical  cyclones  {hurricanes)  for  a  period  of  years. 

Tropical  cyclones  are  stronger  than  those  of  intermediate  latitudes;, 
that  is,  the  pressure  at  the  center  is  lower  and  the  winds  are  higher. 
Many  of  them  do  great  damage  along  coasts,  both  to  shipping  and  to 
low  coastal  lands.     The  great  storm  at   Galveston  in   September, 


92  STORMS  AND  WEATHER  FORECASTING 

1900,  resulted  in  a  loss  of  6,000  lives,  and  damage  to  property  esti- 
mated at  more  than  $30,000,000.  Much  of  the  destruction  was  due 
to  water  driven  by  the  high  winds  over  the  low  island  on  which 
Galveston  stands.  An  expensive  sea-wall  (Fig.  50)  has  since  been 
built,  and  the  level  of  the  city  raised,  to  prevent  the  recurrence  of  such 
a  disaster. 

'  In  September,  1906,  a  West  Indian  hurricane  swept  the  Gulf  coast  of  Florida 
and  Alabama,  and  then  passed  inland,  with  damage  to  shipping  and  crops  estimated 
at  IS  to  25  millions  of  dollars.  Islands  which  lie  near  cyclone  tracks  sufiFer  severely. 
Porto  Rico,  for  example,  has  been  devastated  five  times  within  the  last  century. 
The  storm  of  1899  was  probably  the  worst.  Coflfee,  sugar-cane,  and  tobacco  crops 
were  destroyed  almost  completely,  more  than  3,300  lives  were  lost,  and  the  property 


Fig.  50.     A  cross-section  of  the  Galveston  sea-wall,  showing  plan  of  construe' 
tion  and  relative  dimensions.      The  right-hand  side  faces  the  sea. 


damage  was  estimated  to  be  not  less  than  $35,000,000.  During  this  storm  23 
inches  of  rain  fell  in  24  hours.  These  tropical  storms  are  so  violent  that  sailing 
vessels  once  within  the  storm's  grasp  rarely  escape.  For  this  reason  there  has  been 
much  careful  study  of  these  storms.  Sailing  directions,  giving  instructions  how  to 
escape  from  them,  are  now  a  part  of  the  equipment  of  every  vessel  frequenting  the 
oceans  where  tropical  cyclones  occur. 

In  the  Atlantic,  tropical  cyclones  occur  north  of  the  equator, 
though  not  south  of  it ;  in  the  Pacific,  they  occur  both  north  and  south. 
They  occur  in  the  later  part  of  the  hot  season,  and  are  believed  to 
originate  in  strong  convection  (p.  38)  currents.  Fortunately  tropical 
cyclones  are  much  less  frequent  than  cyclones  of  middle  latitudes. 


FORECASTING  THE  WEATHER  93 

Weather  Forecasting 

Weather  predictions.  Weather  predictions  are  based  on  the 
facts  shown  on  weather  maps.  As  a  rule,  official  predictions  are 
made  only  for  the  36  or  48  hours  immediately  following  the  hour  when 
the  map  is  made.  Take,  for  example,  the  map  of  the  25th  of  Septem- 
ber, 1903  (Fig.  46).  Rain  accompanies  the  cyclone  which  is  central 
over  Dakota.  Since  this  storm  has,  for  the  last  24  hours,  been  moving 
a  little  south  of  east  at  the  rate  of  about  40  miles  an  hour,  it  is  fair  to 
presume  that  it  will  move  in  this  same  general  direction  at  a  similar 
rate  for  the  next  24  hours.  If,  in  this  time,  it  advances  to  the  Lake 
Superior  region,  it  probably  will  bring  with  it  weather  similar  to  that 
which  it  is  now  giving  to  the  region  where  it  occurs.  Hence,  on  the 
25th,  the  prediction  might  be  made  that  rain  is  to  be  expected  in 
about  24  hours  in  the  region  around  the  head  of  Lake  Superior. 

On  the  26th  the  prediction  might  be  made  that  the  low  which  js 
central  north  of  Lake  Superior  (Fig.  47)  will  move  on  to  the  Gulf  of 
St.  Lawrence  by  the  succeeding  da,y,  and  that  increasing  cloud- 
iness and  rain  will  accompany  it.  Rain  for  the  region  about  Lake 
Huron  and  the  area  east  of  it  may,  therefore,  be  predicted  for 
the  27th. 

Temperature  changes  as  well  as  changes  in  cloudiness  and  precipi- 
tation may  be  predicted.  Thus  in  Fig.  45  the  isotherm  of  50°  bends 
southward  notably  in  the  high,  central  over  Iowa.  As  the  high  moves 
east,  it  probably  will  carry  the  low  temperature  with  it.  Hence 
it  is  safe  to  predict  that  the  temperature  will  fall  in  the  area  into 
which  the  anticyclone  is  to  move.  The  map  of  the  succeeding  day 
(Fig.  46)  shows  that  the  temperature  of  western  Virginia  has  fallen 
from  about  60°  to  about  40°  along  the  path  of  the  high,  while  areas 
much  farther  north  are  warmer. 

Fig.  46  also  shows  that  North  Dakota  and  Alberta  have  a  tempera- 
ture of  50°,  that  is,  a  temperature  10°  warmer  than  that  of  western 
Virginia.  It  will  be  noted,  too,  that  the  relatively  high  temperature 
of  Dakota,  Montana,  and  Alberta  goes  with  a  low.  As  the  cyclone 
moves  eastward,  the  temperature  along  its  path  probably  will  rise. 
This  is  shown  by  the  map  of  the  next  day  (Fig.  47),  which  shows  a 
temperature  of  about  50°  north  of  Lake  Superior.  The  same  map 
shows  how  the  isotherm  of  40°  bends  to  the  southward  in  front  of  the 
high  which  is  central  over  western  Montana.  As  the  high  of  Montana 
moves  eastward,  it  will  be  likely  to  carry  a  low  temperature  with  it. 


94  STORMS   AND   WEATHER  FORECASTING 

From  this  map,  therefore,  it  may  be  predicted  that  the  temperature 
in  Nebraska,  Kansas,  Iowa,  and  Missouri  will  be  lower. 

The  time  when  the  rain  which  a  storm  may  bring  to  any  given 
place  will  fall  is  calculated  from  the  rate  at  which  the  storm  is  moving. 
In  the  same  way,  the  prediction  of  the  time  of  arrival  of  a  cold  wave 
which  an  anticyclone  may  bring  is  based  on  the  rate  of  progress  of 
the  anticyclone.  This  rate  is  known  in  advance  by  telegraphic  re- 
ports. Predictions  concerning  the  weather  may  be  made  more  readily 
for  the  central  and  eastern  parts  of  the  United  States  than  for  the 
western  part,  for  the  storms  have  been  under  observ^ation  longer 
before  they  reach  the  central  and  eastern  states. 

Failure  of  weather  predictions.  Weather  predictions,  even 
for  short  intervals,  often  fail.  The  reasons  are  many,  among  them 
the  following:  (i)  Cyclones  and  anticyclones  sometimes  depart 
widely  from  the  courses  they  commonly  take.  In  such  cases,  the 
places  the  storm  was  expected  to  pass  do  not  have  the  weather  which 
was  predicted  for  them.  Thus  a  storm  may  be  in  line  for  St. 
Paul,  to  which  it  is  expected  to  bring  rain  and  a  rising  tem- 
perature; but  instead  of  keeping  its  course,  it  may  turn  off  to  the 
northward,  and  the  rain  which  was  predicted  for  that  city  falls 
farther  north. 

(2)  Storms  change  their  rate  of  advance,  and  so  arrive  earlier  or 
later  than  predicted.  (3)  Storms  sometimes  appear  and  disappear 
without  warning.  (4)  A  storm  sometimes  changes  its  character, 
becoming  weaker  or  stronger.  It  then  does  not  bring  to  the  places 
it  passes  the  weather  predicted  for  them. 

Value  of  weather  forecasts.  In  spite  of  all  mistakes,  the 
warnings  of  storms,  floods,  cold  waves,  etc.,  sent  out  by  the 
Weather  Bureau,  have  been  of  great  benefit.  It  has  been  esti- 
mated that  property  valued  at  $15,000,000  was  saved  in  1897 
by  warnings  of  impending  floods.  In  1910  the  estimated  saving  was 
$1,000,000. 

In  September,  1903,  vessels  valued  at  $585,000  were  held  in  ports  temporarily, 
along  the  coast  of  Florida,  by  storm  warnings.  The  loss  of  the  Boston  steamship 
City  of  Portland,  with  all  on  board,  in  the  great  storm  of  November  28,  1898,  was 
due  to  a  failure  to  heed  storm  warnings  which  kept  all  other  craft  in  port.  Warn- 
ings led  to  the  protection  of  $1,000,000  worth  of  fruit  about  Jaciisonville,  Florida, 
in  1901,  with  an  estimated  saving  of  half  this  amount.  Other  warnings  of  cold  in 
1901  were  estimated  to  have  been  the  means  of  saving  more  then  $3,000,000  worth 
of  property.  Shipments  of  perishable  products,  like  most  fruits,  may  be  damaged 
badly  if  freezing  temperatures  are  encountered  unexpectedly  in  transit.     Mer- 


THUNDER-STORMS  95 

chants  handling  such  products  are  saved  much  trouble  and  inconvenience  by  infor- 
matic'n  from  the  Weather  Bureau  concerning  the  temperatures  for  which  their 
shipments  must  be  prepared. 

The  annual  saving  of  property  in  these  various  ways  exceeds, 
several  times  over,  the  total  cost  of  the  Weather  Bureau. 


Local  Storms 

Thunder-storms.  Thunder-storms  are  frequent  in  the  United 
States.  They  are  most  common  in  warm  regions,  and  in  warm 
seasons.  Further,  they  are  most  common  on  days  which  are  unusually 
warm,  and  during  the  warmer  parts  of  these  days;  but  there  are 
occasional  thunder-storms  in  the  winter,  and  there  are  thunder- 
storms at  night. 

The  first  indication  of  a  thunder-storm  is  usually  a  large  cumulo- 
nimbus cloud,  which,  in  the  zone  of  the  westerly  winds,  generally 
appears  in  the  west.  It  moves  eastward,  and  as  it  reaches  the  place 
of  the  observer,  there  is  usually  a  smart  breeze,  or  thunder-squall, 
rushing  out  before  it.  Shortly  after  the  squall  the  rain  begins  to  fall. 
The  rainfall  may  be  heavy,  and  the  drops  large,  but  the  downpour 
does  not  usually  last  more  than  an  hour,  and  in  many  cases  much  less. 
A  second  thunder-storm  sometimes  follows  close  upon  the  first. 

Lightning  is  due  to  the  discharge  of  electricity  from  one  part  of  a  cloud  to 
another,  from  one  cloud  to  another,  or  from  the  cloud  to  the  ground.  When  light- 
ning discharges  approach  the  ground,  they  seek  exposed  objects  in  some  cases  and 
cause  loss  of  property,  chiefly  through  fire,  and  occasional  loss  of  life.  The  thunder 
following  the  lightning  is  due  to  vibrations  in  the  air  caused  by  the  electrical  dis- 
charge. It  sometimes  happens  that  lightning  at  a  great  distance  lights  the  clouds 
over  a  region  where  the  electric  discharge  itself  cannot  be  seen.  This  lighting  of 
the  clouds  is  often  called  heat  lightning,  because  it  is  more  commonly  seen  in  hot 
weather  than  at  other  times.  The  rainbows  which  accompany  or  follow  many  thun- 
der-storms are  due  to  the  effects  of  the  drops  of  water  in  the  atmosphere  as  the  sun's 
rays  pass  through  them. 

In  middle  latitudes,  most  thunder-storms  occur  during  the  passage  of  cyclones, 
though  they  do  not  accompany  all  cyclones.  They  are  more  common  on  the  south 
sides  of  cyclones  than  elsewhere,  and  many  of  them  occur  at  a  considerable  distance 
from  the  center  of  the  main  storm.  In  middle  latitudes,  most  thunder-storms 
move  from  west  to  east,  while  in  the  zone  of  trade-winds  they  move  from  east  to 
west.  In  both  cases  they  move  with  the  prevailing  winds.  Much  of  the  precipita- 
tion from  summer  cyclones  is  connected  with  thunder-storms.  Hence  localities 
having  most  of  their  rain  during  the  warm  season  depend  largely  on  thunder-storms 
for  moisture.  Not  infrequently  violent  thunder-storms  give  precipitation  in  the 
form  of  hail. 


96 


STORMS  AND   WEATHER  FORECASTING 


Tornadoes.  When  a  convection  current  is  very  strong,  and  has  a 
very  small  diameter,  the  whirl  becomes  so  intense  in  some  cases  as  to 
cause  great  destruction.  A  whirling  storm  of  this  sort  is  a  tornado. 
Tornadoes,  like  thunder-storms,  are  phenomena  of  hot  weather. 
They  are  rather  less  abundant  in  the  later  part  of  the  summer  than  in 
the  earlier  part.  They  are  more  likely  to  occur  in  a  cyclone  than  in 
an  anticyclone.  Tornadoes  are  associated  in  most  cases  with  hot 
days,  and  with  the  warmest  part  of  the  day. 

The  atmospheric  pressure  in  the  center  of  a  tornado  is  usually 
much  lower  than  in  the  center  of  a  cyclone.  In  a  very  strong  tornado, 
the  pressure  at  the  center  may  be  a  fourth  less  than  that  of  its  sur- 
roundings. This  is  one  reason  why  the  tornado  is  so  destructive. 
During  its  passage,  the  pressure  may  be  reduced  from  the  normal 
amount,  14.7  lbs.  per  square  inch,  to  three-fourths  of  this,  or  to  11  lbs. 
per  square  inch.  If  such  a  tornado  passes  over  a  closed  building  in 
which  the  air  pressure  is  2,117  lbs.  per  square  foot,  the  pressure  on  the 
outside  becomes  i  ,584  lbs.  The 
walls  are  therefore  pushed  out 
with  a  force  of  533  lbs.  per  square 
foot,  and  unless  they  are  very 
strong,  they  will  fall,  as  if  the 
building  had  exploded.  In  some 
cases  only  the  weaker  parts, 
such  as  windows,  yield. 

Not  only  is  the  pressure  at  the 
center  of  the  tornado  very  low, 
but  the  area  of  the  low  pressure 
is  very  small.  While  a  cyclone 
may  be  1,000  miles  or  more 
across,  few  tornadoes  exceed 
1,000  feet  in  diameter  at  the  sur- 
face of  the  land,  and  many  are 
only  a  few  yards  wide.  The  re- 
sult is  that  the  winds  are  violent. 
Estimated  by  the  size  and  weight 
of  the  objects  moved,  their 
velocities  have  been  thought  to  reach  400  or  500  miles  per  hour. 
With  this  velocity,  or  even  a  velocity  much  less,  trees  are  over- 
turned, buildings  unroofed  or  blown  down,  and  bridges  hurled  from 
their  foundations. 


Fig.  51.  Funnel-shaped  cloud  of  a 
tornado,  Solomon,  Kas.  (U.  S.  Weather 
Bureau.) 


DESTRUCTION  BY  TORNADOES  97 

A  tornado  is  often  seen  first  as  a  funnel-shaped  cloud  (Fig,  51), 
the  point  of  which  may  be  far  above  the  ground.  As  the  funnel  moves 
forward,  its  lower  end  may  rise  or  fall.  The  cloud  is  due  chiefly  to 
the  condensation  of  moisture  in  the  sharp  convection  current,  and  the 
funnel  shape  is  due  to  the  expanding  and  spreading  of  the  air  as  it 
rises. 

The  tornado  is,  of  all  storms,  the  most  destructive,  but,  in  most 
cases,  it  has  a  very  narrow  track,  and  does  not  work  destruction  for 
a  very  great  distance,  rarely  more  than  15  to  30  miles. 

One  of  the  most  destructive,  though  not  one  of  the  most  violent,  tornadoes  ot 
recent  times  was  that  at  St.  Louis,  May  27,  1896.  It  accompanied  a  thunder- 
storm in  the  southeastern  part  of  a  cyclone,  central  some  distance  northwest  of  the 
city.  The  destruction  of  property  in  and  about  St.  Louis  was  estimated  at  about 
$13,000,000. 

A  more  violent  tornado  was  that  at  Louisville  on  the  27th  of  March,  1890, 
Just  before  nine  o'clock  in  the  evening.  Many  weak  buildings  were  wrecked,  76 
persons  were  killed  and  about  200  injured  in  Louisville  alone,  and  the  loss  of  prop- 
erty was  estimated  at  about  $2,500,000. 


Questions 

1.  Explain  the  apparent  contradiction  in  the  fact  that  northeast  winds,  in 
most  areas  of  the  United  States,  are  part  of  a  storm  coming  from  the  west. 

2.  Show  by  a  series  of  diagrams,  in  their  proper  order,  the  weather  changes 
which  would  take  place  at  a  given  station  on  three  successive  days  under  the 
following  conditions:  (i)  On  the  first  day  the  storm  center  (low)  is  approaching 
from  the  southwest;  (2)  on  the  second  day  at  noon  the  center  is  200  miles  away, 
directly  to  the  sputh;  (3)  on  the  third  day  it  has  moved  on  in  the  normal  direction, 
and  at  the  normal  rate.     Diameter  of  the  low,  1,000  miles. 

Make  similar  diagrams  for  the  same  place  for  a  storm  following  a  track  200 
miles  to  the  no.th  of  the  station. 

3.  Make  rule=  for  forecasting  temperature  when  the  weather  map  shows 
isotherms  running  (i)  east  and  west,  and  far  apart;  (2)  north  and  south,  and  close 
together. 

4.  Indicate  what  truth,  if  any,  there  is  in  the  following  weather  proverbs: 
(i)  "Too  cold  to  snow."  (2)  "A  white  frost  is  a  sign  of  a  fair  day  to  follow." 
(3)  "Rainbow  in  the  morning,  sailors  take  warning;  rainbow  at  night,  the  sailors 
delight." 

5.  Suggest  other  weather  proverbs  which  you  have  heard,  and  show  whether 
or  not  they  have  any  basis  of  truth. 

6.  Why  are  large  dealers  in  grains,  cotton,  and  tobacco  interested  in  the  daily 
weather  map? 

7.  Suggest  some  of  the  changes  in  the  climate  of  the  United  States  which 
would  result  (i)  if  the  Rocky  Mountains  ran  east  and  west,  along  the  entire  length 
of  the  Canadian  boundary;   (2)  if  the  area  of  the  Gulf  of  Mexico  were  land. 


CHAPTER  IX 
TROPICAL  CLIMATE 

Extent  of  tropical  regions.  The  tropical  zone,  as  usually  defined, 
is  limited  by  the  tropic  of  Cancer  on  the  north  and  the  tropic  of 
Capricorn  on  the  south.  Other  definitions  of  this  zone  have  been 
suggested,  as  (i)  the  zone  where  the  trade-winds  blow,  and  (2)  the 
zone  where  the  palm  tree  grows,  the  palm  being  taken  as  the  type  of 
tropical  vegetation  (Fig.  52).  Defined  by  parallels,  the  tropical 
zone  covers  about  two-fifths  the  area  of  the  earth. 

About  one-third  of  all  the  land  —  in  round  numbers,  17,000,000 
square  miles  —  is  within  the  tropics.  This  third  of  the  land  sup- 
ports about  a  third  of  the  people  of  the  earth  —  in  round  numbers, 
500,000,000.  Much  tropical  land  is  desert,  and  much  is  covered 
with  dense  forests  (Fig.  53),  and  these  parts  are  but  sparsely  peopled; 
but  the  fertile  areas  which  are  cultivated  support  dense  populations. 
In  Java,  for  example,  30,000,000  people  live  in  an  area  two-thirds 
that  of  Pennsylvania.  About  one-seventh  of  North  America  and 
one-sixth  of  its  people  are  in  the  tropics.  The  tropical  part  of  South 
America  is  much  larger,  nearly  three-fourths  of  the  continent  and  of  its 
people  being  between  the  Caribbean  Sea  and  the  tropic  of  Capricorn. 
No  part  of  Europe  is  in  the  tropics,  and  only  about  one-fifth  of  Asia  is 
tropical,  but  this  fifth  supports  fully  half  the  population  of  the  conti- 
nent. Three-fourths  of  Africa  are  in  the  tropical  zone  and  two-thirds 
of  its  people,  and  about  half  of  Australia  and  one-fourth  of  its  people. 

The  area  of  ocean  within  the  tropics  is  about  70,000,000  square 
miles.  The  large  proportion  of  water  in  this  zone  gives  much  of 
the  land  a  marine  climate.  Relatively  small  areas,  in  the  wider 
parts  of  the  continents,  show  true  continental  conditions. 

General  Characteristics  of  Tropical  Climates 

The  most  striking  thing  about  the  climate  of  tropical  regions 
is  its  uniformity.  The  weather  does  not  change  frequently,  as  in 
middle  latitudes.     Atmospheric  conditions  are  so  nearly  uniform 

98 


TEMPERATURE   CONDITIONS  IN  THE  TROPICS 


99 


month  after  month  that  weather  and  cli- 
mate are  almost  the  same.  Now  and  then 
hurricanes  and  typhoons  occur  in  some 
parts  of  the  zone. 

Uniformity  of  temperatures.  The 
temperatures  of  the  tiopics  are  even  more 
uniform  than  the  other  elements  of  cli- 
mate, (i)  The  noon  altitude  of  the  sun 
varies  much  less  than  in  other  zones,  and 
(2)  the  length  of  day  and  of  night  is  always 
nearly  the  same.  As  a  result,  the  amount 
of  insolation  never  varies  much,  and  since 
it  is  always  large,  the  temperature  is 
always  high,  except  at  high  altitudes. 

Annual  changes.  Many  tropical 
places  have  a  range  of  less  than  10° 
between  the  mean  temperatures  of  the 
warmest  and  coldest  months,  and  a  range 
of  less  than  15°  is  characteristic  of  most 
tropical  lands.  On  the  oceans,  and  on 
some  lands,  the  range  is  insignificant.  At 
Bogota,  Colombia,  the  coolest  month  is 
less  than  3°  cooler  than  the  warmest. 
Buitenzorg,  Java,  has  an  annual  range  of 
only  1.8°.  Toward  the  edges  of  the 
tropical  zone,  the  annual  range  of  tem- 
perature is  greater,  especially  inland. 
Thus  at  Nagpur,  in  the  interior  of  India, 
Lat.  2i°9',  the  range  is  27.1°. 

Diurnal  changes.  In  many  parts  of 
the  tropical  zone,  the  difference  in  tem- 
perature between  day  and  night  is  greater 
than  that  between  the  warmest  and  the 
coolest  months.  Near  coasts,  the  tem- 
perature rarely  falls  below  70°  at  night,  or 
rises  above  90°  by  day.  Inland,  the  range 
is  much  greater,  and  in  dry  regions  far 
from  coasts  it  is  as  much  as  60°  or  70°  in 
some  places  (from  50°  or  60°  at  night,  to 
a  maximum  of  120°  by  day).    In  places. 


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fieezing  temperatures  have  been  known  at 
sea-level,  as  in  deserts  near  the  margins  of 
the  zone.  Since  the  daily  range  is  several 
times  as  great  as  the  range  between  the 
warmest  and  coldest  months,  it  is  a  common 
saying  that  "night  is  the  winter  of  the 
tropics."  The  daily  range  is  much  the  same 
day  after  day. 

On  the  whole,  the  highest  temperatures 
of  the  tropics  are  no  higher  than  those  of 
middle  latitudes.  It  is  not  so  much  the 
high  temperature,  as  the  continued  high 
temperature,  which  distinguishes  tropical 
climate. 

Effects  of  temperatures.  Seasonal 
changes  of  temperature  are  so  slight  that 
they  have  little  influence  on  life  —  animal 
or  plant.  The  likeness  of  one  day  to 
another,  and  of  one  month  to  another,  is 
probably  a  chief  cause  of  the  habit  which 
tropical  people  have  of  putting  oflf  every- 
thing possible  until  "tomorrow." 

In  some  parts  of  the  tropical  zone,  high 
temperatures  are  associated  with  high 
humidity.  This  means  a  high  sensible  tem- 
perature, which  is  uncomfortable  and  harm- 
ful in  various  ways.  Sunstrokes  and  heat 
prostrations  are  especially  common  among 
white  people.  The  high  temperature  and 
humidity  are  also  unhealthful,  and  together 
constitute  one  of  the  greatest  obstacles  to 
the  life  of  white  men  in  this  zone.  The 
dampness  and  heat  are  enervating,  as  illus- 
trated by  the  general  laziness  of  tropical 
natives  (p.  337)  —  a  trait  which  appears 
sooner  or  later  in  most  white  people  who 
remain  in  this  zone. 

One  of  the  most  important  results  of  the 
high  temperature  of  tropical  regions  is  that 
it  permits  vegetation  to  grow  throughout 


RAINFALL  IN  THE  TROPICS  loi 

the  year,  where  rainfall  is  sufficient.  Many  trees  bear  buds,  blossoms, 
and  ripe  fruit  at  the  same  time. 

Variability  of  rainfaU.  The  variability  of  tropical  rainfall  is  in 
contrast  with  the  uniformity  of  the  temperature.  Some  places  are 
always  dry,  and  others  always  rainy.  In  some  places  there  is  no 
rain  for  months  at  a  time,  and  almost  daily  rains  during  the  rest  of  the 
year.  Some  places  have  one  rainy  season  each  year,  while  others 
have  two.  This  variability  of  rainfall  is  the  controlling  factor  in  the 
climate  where  the  other  leading  element,  temperature,  is  nearly  con- 
stant.    In  general,  the  variations  of  rainfall  are  definite  and  regular. 

The  distribution  of  rain  in  the  tropics  is  influenced  by  (i)  winds, 
and  (2)  topography.  The  winds  (and  calms)  most  important  in  deter- 
mining the  distribution  of  rains  are  (a)  the  trade-winds,  and  (b)  the 
equatorial  calms  (p.  74).  The  calm  belt  moves  north  and  south 
after  the  sun  (p.  14),  and  its  movement  afifects  the  position  and  ex- 
tent of  the  trade-wind  belts.  The  periodic  character  of  rains  in  this 
zone  depends,  therefore,  mainly  on  the  apparent  movement  of  the 
sun  north  and  south  of  the  equator. 

Seasons  of  rainfall.  For  most  places  within  the  limits  of  the 
migrating  belt  of  calms,  the  rain  comes  when  the  sun  is  nearly  over- 
head, or  a  little  later.  In  the  trade-wind  zone,  as  elsewhere,  rain 
is  likely  to  fall  from  air  forced  up  over  high  elevations  (p.  77). 

The  distribution  of  rainfall  through  the  year  gives  a  basis  for  the 
division  of  the  year  into  seasons.  Some  places  have  two  seasons,  one 
rainy  and  one  dry,  while  others  have  four  seasons,  two  rainy  and  two 
dry.     The  lengths  of  these  seasons  vary  much  from  place  to  place. 

Effects  on  life.  Rainfall  is  here  the  chief  factor  controlling  the 
distribution  of  life,  and  many  of  its  relations.  This  is  illustrated 
(i)  by  the  rapidity  with  which  vegetation  springs  up  when  rain  begins 
after  a  long  dry  season;  (2)  by  the  fact  that  over  millions  of  square 
miles  the  planting  of  crops  depends  on  the  coming  of  rain;  and  (3) 
by  the  further  fact  that  even  the  nesting  of  many  birds  takes  place 
only  in  the  rainy  season. 

Types  or  Climate  within  the  Tropics 

Rainfall  and  its  effects  furnish  a  basis  on  which  different  types  of 
tropical  climate  may  be  distinguished.  There  are  four  principal 
types:  (i)  The  equatorial  type,  affecting  a  zone  of  10°  to  15°  on 
either  side  of  the  equator;  (2)  the  trade-wind  type,  affecting  belts  be- 


I02  TROPICAL   CLIMATE 

tween  the  equatorial  zone  and  the  tropics  of  Cancer  and  Capricorn; 
(3)  the  monsoon  type,  especially  about  lands  near  the  sea;  and  (4)  the 
modification  of  these  types  produced  by  high  altitudes,  giving  what 
may  be  called  mountain  climate. 

I.  Equatorial  Climate 

Temperature.  Temperature  is  least  variable  in  the  equatorial 
part  of  the  tropical  zone.  The  differences  of  temperature  here 
depend  chiefly  on  (i)  nearness  to  the  sea,  especially  nearness  to  that 
sea  from  which  the  wind  blows  to  the  land,  and  (2)  altitude.  The 
tj^ical  marine  climate  of  this  belt  has  almost  no  change  of  tempera- 
ture from  month  to  month.  Thus  Batavia,  the  capital  of  Java,  has  a 
mean  annual  temperature  of  78.8°  F.,  and  the  coolest  month  is  only  2° 
cooler  than  the  warmest.  In  the  interior  of  central  Africa,  on  the  other 
hand,  the  mean  annual  temperature  may  be  the  same  as  that  at  Bata- 
via, but  from  the  warmest  to  the  coolest  month  the  range  is  10°  or  12°. 

The  daily  range  of  temperature  is  almost  always  greater  than 
the  annual  range.  Quito,  Ecuador,  Lat.  o°i4'  S.,  at  an  altitude  of 
9,350  feet,  has  an  annual  range  of  less  than  1°;  but  throughout  the 
year  the  temperature  in  early  morning  is  about  47°,  while  at  midday 
it  is  about  66°.  On  coasts  and  low  islands  in  similar  latitudes,  the  daily 
range  is  less,  say  from  90°  to  75°.  People  living  under  the  latter 
conditions  are  very  sensitive  to  marked  changes  of  temperature,  and 
for  them  a  temperature  much  below  70'  may  mean  actual  suffering. 
Frost  on  low  lands  near  the  sea  is  unknown. 

Rainfall.  The  rains  come,  for  the  most  part,  in  daily  showers. 
Even  during  the  season  of  greatest  rain,  almost  every  day  has  a  clear 
morning,  and  the  rain  comes  from  thunder-storms  in  the  afternoon. 
In  many  places  they  come  with  marked  regularity  at  a  certain  hour 
in  the  afternoon. 

The  migration  of  the  belt  of  calms  involves  the  movement  of  the 
zone  of  daily  thunder-storm  rains.  All  places  alternately  in  and  out 
of  the  belt  of  calms  have  wet  and  dry  seasons.  Near  the  borders  of 
the  equatorial  region  there  is  one  short  wet  season  and  one  long  dry 
one.  In  the  central  part  of  the  region  there  are  two  wet  and  two  dry 
seasons,  but  the  latter  are  not  so  dry  as  those  farther  from  the  equator. 

The  rainfall  of  places  near  the  margin  of  the  equatorial  belt  is 
illustrated  by  that  at  Cochabamba,  Bolivia,  17°  20'  S.,  which  has 
plentiful  rain  during  its  summer  (December  to  February),  and  a  nearly 
rainless  season  from  the  middle  of  March  to  the  middle  of  November. 


/ 


EQUATORIAL   CLIMATE   AND   LIFE  103 

North  of  the  equator,  in  the  latitude  corresponding  to  that  of 
Cochabamba,  the  rainy  season  begins  in  May  or  June,  and  continues 
until  September  or  October.  Since  there  is  Httle  difference  in  tem- 
perature between  the  various  months  of  the  year,  the  value  of  rain- 
fall for  crops  is  about  as  great  at  one  time  as  another.  On  the  whole, 
rainfall  near  the  equator  is  (i)  more,  and  (2)  less  variable  in  amount, 
time  of  coming,  and  duration,  than  rainfall  nearer  the  borders  of  the 
equatorial  belt.  As  a  rule,  the  farther  a  place  in  this  belt  is  from 
the  equator,  the  shorter  its  rainy  season. 

Humidity  and  cloudiness.  Humidity  is  high,  as  a  rule,  during 
the  rainy  season,  and  low  during  the  dry  season.  While  continued 
high  humidity  has  bad  effects  on  tropical  people,  as  already  pointed 
out,  it  favors  hea\y  dews,  which  may  be  of  great  benefit  where  rainfall 
is  scanty.  Cloudiness  is  common  during  the  rainy  seasons,  and 
where  there  are  two  rainy  seasons,  there  may  be  cloudiness  70  or  80 
per  cent  of  the  time. 

The  distribution  of  rain  and  clouds  throughout  the  year  affects 
the  temperatures  of  the  different  months.  As  a  rule,  the  end  of  the 
dry  season  has  the  highest  temperature,  and  the  rainy  season  is,  in 
many  places,  the  coolest  part  of  the  year,  though  the  sun  is  then 
highest.  This  is  due  to  the  fact  that  the  clouds  shut  off  the  sun's 
rays  for  a  considerable  part  of  the  day.  The  increased  humidity  of 
the  rainy  season  may  make  its  sensible  temperature  higher  than 
that  of  the  hotter  dry  season.  In  many  places,  therefore,  the  rainy 
season  is  the  most  disagreeable  time  of  year.  Some  tropical  diseases 
are  also  most  prevalent  then. 

Moist  equatorial  climate  and  life.  The  high  temperature  of 
this  zone  and  the  abundant  rainfall  of  its  central  portion  favor  a 
luxuriant  growth  of  vegetation.  Dense  forests,  such  as  those  in  the 
Amazon  Valley,  in  central  Africa,  and  in  the  Malay  Peninsula,  are 
characteristic  of  the  humid  parts  of  the  zone.  These  forests  are 
inhabited  only  by  relatively  sparse  populations  of  backward  natives, 
who  live  chiefly  by  hunting  and  fishing,  and  on  the  food  supplied  by 

the  forest  (pp.  337-339)- 

The  moist  equatorial  climate  is  unhealthful,  especially  for  white 
people.  Tropical  malaria,  yellow  fever,  and  intestinal  disorders  are 
the  worst  enemies  which  the  white  man  meets  near  the  equator.  All 
these  reach  their  maximum  during  the  rainy  season.  The  first  two 
are  spread  by  mosquitoes,  and  consequently  are  associated  with  wet, 
swampy  places. 


I04  TROPICAL   CLIMATE 

Along  the  Amazon  Valley,  and  especially  on  the  equatorial  coast  of  Africa, 
fevers  almost  control  the  location  of  residences  for  white  settlers.  If  the  white 
man  escapes  the  fevers,  there  is  still  the  climate  itself  with  which  he  must  contend. 
The  never-varying  high  temperature,  and  the  excessive  moisture  month  after 
month,  with  never  any  stimulus  from  invigorating  cold,  gradually  have  their 
efifect.  Tropical  anaemia  appears  sooner  or  later  in  most  cases,  and  unless  he  seeks 
relief  in  a  colder  climate,  the  white  man  loses  his  physical  and  mental  vigor. 

It  is  necessary  to  employ  a  force  of  men  simply  to  keep  the  tracks  of  some  trop- 
ical railroads  clear  of  vegetation.  Many  wagon  roads  become  impassable  in  the 
rainy  season,  and  at  these  times  a  mud  sledge,  hauled  by  the  water  buffalo,  is  used 
in  some  regions,  but  it  is  a  very  primitive  and  unsatisfactory  mode  of  conveyance. 
During  the  rainy  season  the  rivers  are  swollen,  and  travel  by  boat  is  easier  than  at 
other  times,  for  great  sections  of  country  are  then  flooded. 

Wooden  railroad  ties  and  telegraph  poles  decay  rapidly,  and  it  is  necessary,  in 
building  railroads  in  pa'-ts  of  the  tropics,  to  use  special  woods,  which  do  not  decay 
readily,  or  to  substitute  iron  and  concrete.  The  effect  of  all  these  things  is  to  retard 
commerce.  The  most  favored  localities  for  trade  in  equatorial  regions  are  those 
where  a  large  river  offers  a  natural  trade  route,  and  the  river  port  is  therefore  the 
commercial  center.  Para  and  Manaos,  on  the  Amazon,  are  examples  of  cities 
developed  by  river  traffic  through  an  equatorial  forest.  The  commodities  handled 
are  largely  forest  products  (p.  339). 

Dry  equatorial  climate  and  life.  Toward  the  borders  of  the 
region  of  equatorial  climate  the  absence  or  scantiness  of  rain  through 
most  of  the  year  leads  to  vegetation  very  different  from  that  nearer 
the  equator.  Grass  lands  re]>lace  dense  forests  (Fig.  53),  the  llanos 
of  Venezuela,  the  campos  of  Brazil,  and  the  Sudan  of  Africa,  being 
good  examples.  These  regions  are  without  large  forests,  since  the 
period  of  growth,  limited  chiefly  to  the  rainy  season,  is  too  short  for 
trees.  Scattered  patches  of  forest,  however,  occur  here  and  there, 
as  in  the  campos  of  Brazil. 

The  people  of  the  grass  lands  are  more  advanced  than  the  forest-dwellers  nearer 
the  equator.  They  get  much  of  their  living  from  flocks  and  herds.  The  necessity 
of  moving  frequently  to  find  new  pasturage  for  their  cattle,  goats,  or  camels,  makes 
many  of  these  pastoral  people  nomadic. 

In  favored  places,  especially  where  irrigation  is  possible,  the  people  become 
permanent  settlers,  and  cultivate  the  soil.  Outside  the  irrigated  lands,  crops  are 
planted  to  some  extent,  but  only  in  the  rainy  season,  and  only  where  the  rainfall  is 
considerable.  Sometimes  the  rain  fails  to  come  at  the  expected  time,  or  in  the 
amounts  expected.  This  uncertainty  has  retarded  the  development  of  agriculture, 
and  has  led  to  frequent  famines. 

Irrigation  may  yet  make  productive  much  dry  land  in  this  cli- 
mate. Here  white  men  may  live  with  more  comfort  than  nearer 
the  equator,  for  the  low  humidity  during  much  of  the  year  is  more 
healthful,  and  makes  the  high  temperature  easier  to  bear.     The  llanos 


CLIMATE  OF  TRADE-WIND   BELTS  105 

of  Venezuela,  the  campos  of  Brazil,  and  the  African  Sudan  are  there- 
fore important  regions  with  respect  to  future  development. 

2.  Trade-Wind  Climate 

Winds  and  temperature.  The  most  striking  feature  of  the 
trade-wind  climate  is  the  steadiness  of  the  winds,  which  blow  with 
a  velocity  of  10  to  30  miles  an  hour  throughout  the  year.  The  steady 
winds  make  the  temperature  conditions  simple,  especially  over  the 
oceans,  and  the  climate  of  islands  which  He  in  the  trade-wind  zone 
is  about  the  simplest  in  the  world. 

Both  annual  and  diurnal  changes  of  temperature  are  greater 
than  in  the  equatorial  belt.  Low  lands  swept  by  the  trades  tend 
to  be  arid.  They  are  warmed  rapidly  by  day,  and  cooled  rapidly 
at  night,  having  in  many  places  a  daily  range  of  50°  or  60°.  Tem- 
peratures as  low  as  32°  are  not  unknown.  These  great  changes  are 
felt  less  than  equal  changes  near  the  equator,  because  the  humidity 
is  low.  The  drier  air  with  its  greater  changes  of  temperature  makes 
the  arid  and  desert  lands  more  healthful  than  moist  equatorial  re- 
gions. In  some  ways  the  desert  climate  is  invigorating,  and  diseases 
common  in  the  equatorial  regions  are  rare  in  many  trade-wind  dis- 
tricts. Man  does  not  encounter  the  same  kinds  of  difl&culties,  there- 
fore, as  in  the  equatorial  regions. 

Rainfall.  Though  commonly  drying  winds,  the  trades  contain 
much  water  vapor,  and  become  wet  winds  when  cooled  to  the  dew 
point.  They  are  not  so  cooled  over  low  lands,  hence  the  latter  are 
dry  as  long  as  the  trades  blow.  Where  they  blow  throughout  the  year, 
the  land  is  desert  (Fig.  39).  On  the  other  hand,  where  the  trades 
blow  over  high  lands,  the  ascending  air  is  cooled,  and  clouds  may 
form  and  rain  fall.  For  this  reason,  the  windward  sides  of  highlands 
in  the  trade-wind  belts  are  likely  to  be  rainy,  while  the  leeward  sides 
are  dry  (Fig.  39).  The  leeward  (westward)  side  of  the  Andes,  from 
Ecuador  to  northern  Chile,  presents  the  strange  spectacle  of  a  coastal 
desert,  and  a  similar  condition  is  found  on  the  leeward  coast  of  south- 
west Africa.  Highlands  standing  in  mid-ocean  also  have  a  rainy  side 
toward  the  trades,  and  a  drier  side  m  the  lee,  as  illustrated  by  the 
Hawaiian  Islands. 

In  Australia  (Fig.  54),  a  continuous  highland  Hes  close  to  the  east  coast, 
directly  across  the  path  of  the  southeast  trades.  The  effect  of  this  barrier  is  to 
increase  the  area  of  the  interior  desert,  sometimes  called  the  "dead  heart  of  Aus- 
tralia," and  greatly  to  restrict  the  spread  of  population  (Fig.  55). 


io6 


TROPICAL   CLIMATE 


The  importance  of  high  lands  in  getting  rain  from  trade-winds  is  seen  in  the 
fact  that  rain  falls  and  vegetation  flourishes  (p.  334)  on  local  elevations  in  the 
Sahara.     Streams  flow  for  short  distances  from  the  mountains,  but  soon  dry  up  or 

are  absorbed  into  the  sands  oi 
the  desert  below. 


li 


Fig.  54- 


Fig 
tralia. 


rainfall    for   Aus- 


Fig.  55- 
54.     Mean   annual 
(Diercke.) 
Fig.   55.     Map   showing   density  of   popu- 
lation per  square  mile  in  Australia.     (Lyde.) 


Most  low  lands  aflfected 
by  the  trades  are,  on  the 
whole,  sunny,  and  trade- 
wind  deserts  are  almost 
cloudless.  This  fact  may 
have  significance  in  the 
future,  in  the  possible 
generation  and  storage  of 
power  derived  from  the 
heat  of  the  sun's  rays. 
Cloudiness  is  confined 
chiefly  to  windward 
slopes,  which  form  but  a 
small  part  of  the  total  area 
of  the  trade-wind  zone. 

The  time  of  the  rains 
in  the  trade-wind  belts 
varies  from  place  to  place. 
In  some  places  it  is  dis- 
tributed somewhat  evenly 
throughout  the  year;  in 
others  it  is  seasonal. 
Places  which  get  rain 
from  the  trade-winds 
have  no  rainless  season 
if  the  winds  are  steady 
throughout  the 


g..^^.  ...^  year,  as 
in  the  central  parts  of  the 
trade-wind  zones.  The 
trade-wind  type  of  rain- 
fall is  modified  in  latitudes  low  enough  to  be  reached  by  the  equatorial 
calms.  Trade-winds  are  interrupted  in  some  places  by  monsoon  winds 
(p.  75),  and  where  this  is  the  case,  they  may  modify  rainfall  conditions. 
Cyclones.  The  normal  weather  conditions  of  trade-wind  belts 
are  in  places  interrupted  by  tropical  cyclones.    They  appear  to  origi- 


TRADE-WIND   CLIMATE   AND   LIFE  107 

nate  along  the  margins  of  the  equatorial  belt,  and  move  to  higher  lati- 
tudes through  the  trade- wind  zone  (Fig.  49).  They  occur  during  late 
summer  and  early  autumn  only.  They  interfere  with  the  regular  daily 
changes  of  temperature,  and  in  many  cases  they  give  torrential  rains. 
Trade-winds  and  commerce.  The  steady,  reliable  trade-winds, 
which  prevail  over  a  wide  east-west  belt  of  the  oceans,  have  long 
helped  to  determine  the  courses  of  sailing  vessels,  whose  routes,  going 
and  commg,  are  different. 

Whaling  vessels  out-bound  to  the  Pacific  from  New  Bedford  commonly  went 
across  the  Atlantic  to  the  Cape  Verde  or  Canary  Islands  before  turning  south. 
Vessels  in-bound  from  the  Pacific  to  New  England  usually  swing  around  Cape 
Horn,  far  out  into  the  South  Atlantic  (Why?),  and  then  sail  directly  home. 
The  Panama  Canal  will  be  of  little  importance  to  sailing  vessels  going  east,  on  ac- 
count of  adverse  winds.  Similarly,  the  Red  Sea  presents  head  winds  to  sailing  ves- 
sels going  from  the  Indian  Ocean  to  the  Mediterranean.  Unlike  sailing  vessels, 
steamers  generally  follow  about  the  same  course  in  both  directions. 

Trade-wind  climate  and  life.  Temperature  conditions  are  al- 
most as  favorable  for  vegetation  in  the  trade-wind  zone  as  in  the 
equatorial  belt,  but  moisture  is  scanty.  Forests  as  dense  as  those  in 
equatorial  climates  occur  on  the  windward  slopes  of  some  mountains. 
Most  low  lands  in  the  zone  of  trades  are  arid.  The  Sahara,  more 
than  two-thirds  the  size  of  the  United  States,  is  an  example. 

Considering  the  tropical  zone  as  a  whole,  vegetation  decreases 
in  amount  from  the  equator  out  (Fig.  53).  This  is  illustrated  well 
in  Africa,  which  extends  well  beyond  the  tropics  both  north  and 
south  of  the  equator.  Near  the  equator,  there  is  the  dense  equa- 
torial forest,  and  on  either  side  of  it  are  belts  of  grasses,  developed 
best  in  the  Sudan.  North  of  the  Sudan  is  the  Sahara,  with  little  or 
no  vegetation.  South  of  the  equator,  in  the  area  corresponding  to 
the  Sahara,  the  continent  is  narrower  and  the  land  higher,  so  that 
desert  conditions  are  not  as  fully  developed. 

Human  life  in  the  desert  is  controlled  mainly  by  the  climate 
(p.  332).  Vegetation  is  so  scanty  that  the  people,  depending  for  sup- 
port mainly  on  a  few  animals,  must  move  frequently  from  one  source 
of  water  to  another.  Deserts  interfere  in  many  ways  with  travel 
and  communication  among  men,  and  a  desert  is  almost  as  effective  a 
barrier  as  an  ocean  to  plants  and  animals  (p.  331).  Few  beasts 
of  burden  can  stand  desert  conditions,  and  caravan  trade  is  carried 
on  chiefly  with  the  help  of  camels  (p.  331).  Food  and  useful  materials 
of  all  kinds  are  scarce,  yet  the  great  daily  changes  of  temperature 


io8  TROPICAL   CLIMATE 

necessitate  more  clothing  than  is  needed  nearer  the  equator.  White 
clothing  is  worn  most,  because  it  absorbs  less  sun-heat  than  dark 
fabrics.  The  clothing  is  loose,  partly  because  such  clothing  is  more 
comfortable  in  the  heat,  and  partly  because  the  danger  of  dust-storms 
makes  it  desirable  to  have  a  covering  which  can  be  drawn  over  the 
head  quickly  (p.  201).  The  people  of  deserts  usually  live  in  tents, 
or  in  loosely  built,  low,  flat-roofed  houses.  There  is  no  need  for 
shutting  out  cold  or  rain,  and  when  strong,  the  flat  roofs  are  good 
places  to  sleep. 

Since  fuel  is  scarce  in  the  desert,  cooking  is  of  the  most  primitive 
sort.  Much  of  the  little  meat  used  is  air-dried.  Utensils,  such  as 
vessels  for  holding  water,  are  made  of  leather  —  about  the  only 
serviceable  material  to  be  had  in  many  places. 

In  parts  of  the  deserts,  showers  occur  now  and  then.  In  some 
places  they  come  regularly  at  certain  seasons  of  the  year,  and,  in 
favored  spots,  the  rainfall  is  enough  to  grow  grain.  In  this  case, 
the  rainfall  has  a  marked  effect  on  the  customs  and  religions  of  the 
people.  In  some  places  elaborate  ceremonies  are  performed  in  honor 
of  the  rain  gods  before  seeds  are  planted.  The  worship  of  rain, 
of  rain  clouds,  or  of  the  gods  supposed  to  control  them,  is  common. 
Sun  worship  is  also  common,  for  the  sun  is  one  of  the  most  prominent 
things  of  the  desert. 

3.     Monsoon  Climate 

Rainfall.  At  the  season  when  the  sun's  altitude  is  greatest, 
the  trade-winds  are  overcome,  in  some  places,  by  the  tropical  mon- 
soon (p.  75).     While  the  monsoon  lasts,  it  may  blow  very  steadily. 

Monsoons  are  well  developed  in  southern  and  southeastern  Asia, 
especially  in  India  and  thence  to  the  China  Sea.  On  the  eastern 
coast  of  Asia,  northward  nearly  to  latitude  50°,  there  is  a  somewhat 
similar  wind  from  the  ocean  in  summer,  which  gives  some  rain  to  the 
land.  For  most  places  in  the  northern  hemisphere,  the  monsoon 
season  is  between  May  and  October.  In  the  southern  hemisphere, 
especially  northern  Australia,  it  is  from  November  to  April.  The 
monsoon  wind  generally  brings  rain,  and  heavy  rain  on  the  windward 
sides  of  high  mountains.  A  fall  of  400  to  500  inches  a  year  occurs  in 
a  few  places.  Since  it  all  falls  in  four  or  five  months,  this  means  a 
daily  rainfall  of  two  to  four  inches  throughout  the  rainy  season. 

The  Indian  monsoon  is  a  southwest  wind,  blowing  from  the  Indian 
Ocean  and  the  Bay  of  Bengal.  Western  and  southwestern  slopes 
therefore  receive  much  rain,  while  the  eastern  coast,  in  the  lee  of  the 


MONSOON  RAINS  109 

Deccan  plateau  and  Eastern  Ghats,  gets  little  rain  while  the  monsoon 
blows.  This  coast  gets  its  rain  when  the  northeast  trade-wind  blows. 
In  northwestern  India  there  is  a  large  desert,  not  reached  by  the  mon- 
soon. Hence  different  parts  of  India  have  different  types  of  rainfall, 
largely  as  a  result  of  the  relation  of  wind  direction  to  topography. 

The  conditions  which  produce  rain  mean  increased  cloudiness, 
and  so  the  rainy  season  may  be  less  hot  than  the  others.  As  a  rule, 
the  highest  temperatures  occur  just  before  the  rainy  season  begins, 
for  at  this  time  the  regular  winds  become  weak  or  fail  altogether. 
During  the  rainy  season,  the  increased  humidity  more  than  offsets 
the  comfort  which  the  slightly  lower  temperatures  might  afford. 

Northern  Australia  (Fig.  54),  and  the  northern  coast  of  the  Gulf 
of  Guinea,  in  west  Africa,  have  distinct  tropical  monsoon  climates, 
but  there  are  no  important  monsoon  districts  in  the  tropical  lands  of 
the  western  hemisphere,  because  the  arrangement  of  land  and  water 
does  not  favor  their  development. 

Importance  of  monsoon  rains.  Monsoon  lands  afford  rather 
easy  conditions  of  life,  so  far  as  the  needs  of  man  are  concerned,  and 
they  contain  the  larger  part,  of  the  population  of  the  tropical  zone. 
India  alone  has  300,000,000  people,  in  an  area  less  than  two-thirds 
that  of  the  United  States. 

The  importance  of  the  monsoon  rain  to  southern  Asia  can  hardly  be  over- 
emphasized. During  the  dry  season  all  vegetation  withers,  and  the  earth  is 
parched  and  dusty.  Hence  the  growing  of  crops  and  the  support  of  the  people 
over  vast  areas  depend  on  the  regular  appearance  of  the  rain-bringing  monsoon. 
Feu:  one  reason  or  another,  the  monsoons  sometimes  fail;  still  oftener  they  do  not 
appear  when  they  should,  or  stop  sooner  than  usual;  and  finally,  they  are  sometimes 
interrupted  during  what  should  be  their  proper  season.  The  failure  of  the  rain 
means  loss  of  crops  and  famine  for  the  dense  populations  of  the  monsoon  districts. 
Famines  usually  leave  hundreds  of  thousands  of  people  in  a  weakened  condition, 
so  that  ravages  of  epidemic  diseases,  like  bubonic  plague  and  Asiatic  cholera,  com- 
monly follow  a  famine.  In  India,  deaths  from  famine  and  disease  have  exceeded  a 
million  in  a  single  year.  So  great  has  been  the  loss  of  life,  in  some  cases,  that  labor- 
ers enough  to  cultivate  the  farms  were  not  left.  The  regions  of  famine  are  the 
regions  of  moderate  rainfall  (30  to  50  inches),  where,  in  normal  years,  there  is  water 
enough  for  the  crops.  In  other  places,  especially  in  southern  China,  too  much  rain 
sometimes  brings  disaster.  Rivers  rise  high  above  their  banks,  destroying  property 
and  life;  and  famines  resulting  from  the  destruction  of  crops,  at  times  cripple 
whole  provinces. 

4.    Climate  in  High  Altitudes 
Effect  on  temperature.     For  most  of  the  tropical  zone,  varying 
altitude  is  the  one  factor  which  causes  important  variations  in  tem- 


no  TROPICAL   CLIMATE 

perature.  The  extent^  of  this  variation  is  suggested  by  the  fact  that 
tropical  mountains  exceeding  16,000  feet  are  snow-capped. 

The  lower  temperatures  found  at  moderate  altitudes  make  pla- 
teaus in  the  tropics  more  agreeable  and  healthful  than  lowlands.  On 
the  Bolivian  plateau,  for  example,  the  daily  temperature  may  range 
from  32°  to  75°  or  80°.  White  people  living  in  the  tropics  seek  the 
highlands,  whenever  possible,  for  residence  (p.  320).  The  effect  of 
the  lesser  heat  even  at  altitudes  of  7,000-8,000  feet  is  not,  how- 
ever, equal  to  an  invigorating  cold  season,  like  the  winter  of  middle 
latitudes.  The  climate  of  tropical  mountains  and  plateaus  is  some- 
what like  the  marine  climate  of  the  temperate  zones. 

Vegetation  and  altitude.  The  vegetation,  native  and  cultivated, 
of  the  higher  altitudes  of  the  tropical  zone  resembles  that  at  lower 
levels  outside  the  tropics.  For  example,  on  tropical  highlands  in 
Bolivia  wheat  and  potatoes  are  common  crops,  whereas  on  most 
tropical  lowlands  they  cannot  be  grown  at  all,  or  not  as  profitably  as 
rice.  There  is  a  gradual  change  with  increase  of  altitude,  from 
products  like  sugar-cane  or  rice  on  the  lowlands,  through  a  belt 
of  temperate-zone  fruits  or  vegetables  at  a  moderate  altitude,  to 
cold-temperate  and  Arctic  tj^es  of  plants,  and  then  to  perpetual 
snow  at  an  elevation  of  about  16,000  feet.  The  snow  and  ice 
on  the  heights  help  to  supply  water  for  irrigation  below.  In 
places,  too,  the  ice  of  the  high  mountains  is  carried  down  to 
settlements  below. 

Population  and  altitude.  An  important  effect  of  the  highland 
temperatures  is  seen  in  the  distribution  of  the  population.  From 
Mexico  to  Bolivia,  most  of  the  highlands  are  well  populated,  and  the 
lowlands  sparsely  (Fig.  56).  The  single  exception  is  Peru,  where 
three-fourths  of  the  people  live  on  the  coastal  lowland,  which  is  dry 
and  healthful.  Many  of  the  chief  cities  are  at  elevations  exceeding 
5,000  feet. 

In  tropical  America,  it  is  common  for  the  chief  city  to  be  on  the 
highland  in  the  interior,  and  for  a  smaller  city,  serving  as  a  com- 
mercial outlet,  to  be  on  the  hot,  damp  plain  close  to  the  sea.  Mexico 
City  and  Vera  Cruz,  Caracas  and  La  Guayra,  Sao  Paulo  and  Santos, 
are  examples.  Outside  the  cities,  the  highlands  are  the  most  thickly 
settled  and  the  best  developed  sections,  while  the  lowlands  have  few 
people,  chiefly  natives,  and  are  but  little  developed.  The  result  is 
that  many  of  the  chief  products  of  tropical  countries  are  not  really 
tropical  in  character. 


LIFE  ON  TROPICAL  HIGHLANDS 


m 


The  decreased  pressitre  of  air  which  goes  with  increased  altitude  is  of  some 
importance  in  the  higher  tropical  lands.  As  a  rule  the  natives  living  at  high  alti- 
tudes (in  Bolivia  up  to  15,000  feet)  have  a  large  lung  capacity,  on  account  of  the 


Fig.  56.     Map  showing  density  of  population  per  square  mile  in  South  Amer- 
ica.   (Lyde.) 

thin  air.  They  are  active  and  well  on  the  highlands,  but  usually  sicken  if  taken  to 
low  lands  to  live.  On  the  other  hand,  natives  of  lowlands  experience  discomfort  at 
high  elevations.     The  ill  effects  of  lessened  pressure  are  rarely  felt  below  5,000  feet. 


112  TROPICAL  CLIMATE 

The  Future  of  the  Tropics 

Because  of  their  more  comfortable  temperature  and  more  health- 
ful conditions,  the  highlands  of  the  tropics  probably  will  be  well 
developed  earlier  than  the  lowlands.  At  altitudes  above  2,000  or 
3,000  feet,  tropical  diseases,  particularly  malaria  and  yellow  fever, 
are  not  prevalent.  Civilized  peoples  can  live  comfortably  at  these 
altitudes,  and  where  they  have  not  already  done  so,  they  are  likely 
to  establish  themselves  in  lands  of  moderate  height  where  there  is 
adequate  water,  and  from  them  direct  the  development  of  the  adjoin- 
ing lowlands,  the  products  and  resources  of  which  are  of  so  much 
importance  to  the  commercial  world. 

Questions 

1.  (i)  If  there  were  low  land  where  the  Gulf  of  Mexico  and  the  Caribbean  Sea 
are,  what  sort  of  climate  would  it  have?  (2)  What  effect  would  such  a  land  area 
have  on  the  climate  of  northern  South  America  and  Central  America? 

2.  Why  are  not  the  highest  temperatures  found  at  the  equator? 

3.  Explain  the  necessary  relation  of  a  place  to  the  equatorial  belt  of  calms,  in 
order  that  it  may  have  two  rainy  and  two  distinct  dry  seasons  yearly. 

4.  Why  is  there  no  desert  in  tropical  South  America  east  of  the  Andes? 

5.  What  changes  would  be  produced  in  the  climate  of  Australia  if  the  main 
mountain  range  were  on  the  west  coast  instead  of  near  the  east  coast? 

6.  Which  of  the  two  important  tributaries  of  the  Nile  (Plate  VI)  is  the  first  to 
be  in  flood  each  year?     Why?     Which  has  the  greater  flood? 

7.  Suggest  reasons  which  might  delay  the  arrival  of  the  Indian  monsoon. 

8.  Explain  the  distribution  of  rainfall  in  Australia  (Fig.  54). 

9.  What  industries  are  likely  to  be  connected  with  the  distribution  of  popula- 
tion and  rainfall  shown  in  Figs.  54  and  55? 

10.  Account  for  the  distribution  of  population  in  Brazil  (Fig.  56). 

11.  Suggest  ways  in  which  the  several  types  of  climate  found  in  the  tropic? 
might  affect  the  character  of  imports  from  the  outside  world. 


CHAPTER   X 

TYPES   OF  CLIMATE   IN   THE  TEMPERATE   (INTERMEDIATE) 

ZONES 

Extent  of  temperate  zones.  The  two  temperate  (or  inter- 
mediate) zones  lie  on  either  side  of  the  tropical  zone.  Defined  by 
latitude,  their  equatorial  limits  are  the  parallels  23^^°  N.  and  S. 
respectively,  and  their  poleward  limits  the  polar  circles,  66>^°  N. 
and  S.  There  is,  however,  no  marked  change  in  climate  as  these 
boundary  lines  are  crossed.  The  intermediate  zones  contain  a 
little  more  than  half  (52.7  per  cent)  the  area  of  the  earth. 

Southern  hemisphere.  The  total  land  area  of  the  south  tem- 
perate zone  is  only  about  4,000,000  square  miles  (Fig.  57),  and  its 
population  not  more  than  20,000,000.  In  other  words,  the  lands  of 
the  south  temperate  zone,  taken  together,  have  an  area  about  one- 
third  larger  than  that  of  the  United  States,  and  a  population  less 
than  one-fourth  as  great. 

About  one-fourth  of  South  America  (1,800,000  square  miles) 
and  about  the  same  proportion  of  its  people  (10,000,000)  are  south 
of  the  tropic  of  Capricorn.  More  than  half  of  Australia  and  about 
three-fourths  of  its  people  (3,000,000)  are  in  the  same  zone.  Because 
of  aridity  this  part  of  Australia  is  less  important  than  the  correspond- 
ing part  of  South  America.  New  Zealand,  but  little  more  than 
100,000  square  miles  in  area,  has  a  population  of  about  a  million. 
About  7  per  cent  of  Africa  lies  south  of  the  tropic  of  Capricorn. 
This  area  (700,000  to  800,000  square  miles)  has  hardly  more  than 
4  per  cent  of  the  people  (5,000,000  to  6,000,000)  of  the  continent. 

The  area  of  ocean  in  the  south  temperate  zone  is  about  twelve 
times  as  great  as  that  of  the  land  (Fig.  57).  Hence  much  of  this 
zone  has  a  marine  climate,  which  is  much  less  variable  than  the 
climates  of  the  north  temperate  zone. 

Northern  hemisphere.  Nearly  half  of  all  land  is  in  the  north 
temperate  zone,  and  the  area  of  land  there  (26,000,000  square  miles) 
is  about  equal  to  that  of  water  (Fig.  58).     In  North  America,  all  the 

113 


114     TYPES  OF  CLIMATE  IN  TEMPERATE  ZONES 


■Jt-A- 


G.^ 


S.2 


United  States  except  northern  Alaska, 
most  of  Canada,  and  part  of  Mexico,  are 
in  this  zone.  So  also  are  nearly  all  of 
Europe,  most  of  Asia,  and  part  of  northern 
Africa.  This  zone  contains  the  greatest 
nations,  and  the  majority  of  civilized  peo- 
ple. Because  of  the  greater  expanse  of 
land,  continental  climates  are  more  pre- 
valent than  in  the  southern  hemisphere. 
Only  in  certain  broad  aspects  can  the 
climates  of  the  northern  and  southern 
intermediate  zones  be  discussed  together. 

General  Characteristics  of  Climates 
OF  the  Temperate  Zones 

Variability.  There  are  several  types 
of  climate  in  these  zones,  and  their  differ- 
ences are  perhaps  as  striking  as  their 
likenesses.  Variability  is  the  distinguish- 
ing feature  of  most  of  them.  They  vary 
in  (i)  temperature,  (2)  direction  and  veloc- 
ity of  wind,  and  (3)  amount  and  distribu- 
tion of  rainfall.  In  general,  the  variability 
is  less  in  the  southern  hemisphere  than  in 
the  northern. 

Sun  influence.  The  fundamental  cause 
of  variability  in  these  zones,  as  contrasted 
with  the  uniformity  of  tropical  climates,  is 
the  great  variation  in  (i)  the  altitude  of 
the  sun  during  the  year,  and  (2)  the  length 
of  day  and  of  night.  The  sun  never  is 
overhead  at  any  place  in  these  zones,  and 
during  at  least  a  part  of  the  year  it  is 
many  degrees  from  the  zenith  at  noon 
(pp.  13-14).  There  are,  accordingly,  great 
differences  in  the  amount  of  heat  received 
at  different  times,  and  the  year  is  divided 
into  seasons  which  vary  much  in  temper- 
ature. 


TEMPERATURES   OF   INTERMEDIATE  ZONES       115 


Winds.  The  prevailing  (westerly) 
winds  of  these  zones  are  much  less  regular 
in  direction  and  velocity  than  the  trade- 
winds  of  the  tropical  zone,  and  are  inter- 
rupted much  by  cyclonic  storms,  which 
vary  greatly  in  frequency  and  strength. 

Temperature  ranges.  The  factors 
noted  above  lead  to  great  variations  of 
temperature  from  day  to  day,  from  season 
to  season,  and  from  place  to  place.  The 
great  and  sudden  variations  of  tempera- 
ture make  the  term  temperate  singularly 
inappropriate  for  these  zones.  The  weather 
at  least  is  often  most  intemperate.  In 
contrast  with  the  conditions  in  the  tropical 
zone  (p.  99),  observations  through  many 
years  are  necessary  to  get  a  correct  idea  of 
the  climate.  The  yearly  range  of  temper- 
ature in  most  places  is  far  greater  than 
the  daily  range. 

In  the  same  latitude,  conditions  vary 
widely  from  place  to  place,  both  with 
respect  to  variation  of  temperature  and  the 
time  of  greatest  heat  and  cold.  Inland, 
the  highest  and  lowest  temperatures  of 
the  year  generally  occur  about  a  month 
behind  the  highest  and  lowest  noon-alti- 
tudes of  the  sun,  and  the  temperatures  of 
the  warmest  and  coldest  months  may  be 
50°  apart,  even  in  middle  latitudes  (as 
Chicago).  Spring  and  autumn  are  much 
alike  so  far  as  temperature  is  concerned. 
Near  the  sea,  the  highest  and  lowest  tem- 
peratures are  about  two  months  after  the 
solstices,  while  spring  is  cold  and  autumn 
is  warm.  The  maximum  temperatures  in 
summer  in  many  cases  exceed  those  of 
some  tropical  stations,  and  the  lowest 
temperatures  in  winter  approach  polar 
cold.     Summer  weather  is  almost  tropical, 


Kfe^ 


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i<i=i 


ii6     TYPES   OF   CLIMATE  IN  TEMPERATE  ZONES 

and  winter  weather  polar,  in  many  parts  of  these  zones.  Weather 
and  climate  are  therefore  very  unlike,  so  far  as  temperature  is 
concerned.  The  average  annual  range,  however,  is  as  low  as  20° 
in  some  places,  even  in  comparatively  high  latitudes.  Hence,  in  this 
zone,  latitude  is  not  a  sure  index  of  climate. 

North  temperate  zone.  The  great  expanses  of  land  lead  to 
marked  contrasts  in  temperature  between  the  two  margins  of  this 
zone,  within  which  some  of  the  highest  as  well  as  some  of  the  lowest 
known  temperatures  occur.  The  mean  annual  range  varies  from  as 
little  as  16°  in  southern  California  (San  Diego,  near  the  sea),  to  as 
much  as  81°  in  northwestern  Canada  (Fort  Chippewyan,  far  from 
the  sea  to  windward). 

Near  the  tropical  margin  of  this  zone,  summers  and  winters  are 
not  extreme,  and  springs  and  autumns  are  long.  Toward  its  pole- 
ward margin,  on  the  other  hand,  the  differences  between  summer 
and  winter  are  great,  and  the  transition  seasons  are  short.  Hence 
the  length  of  the  growing  season  for  plants  differs  greatly  in  different 
parts  of  the  zone,  with  important  effects  on  life. 

The  variations  of  temperature  are  accompanied  by  variations  in 
rainfall.  In  tropical  lowlands,  where  temperatures  always  are  high, 
it  makes  little  difference  to  vegetation  when  rain  comes;  but  where 
there  are  seasons  of  radically  different  temperatures,  rain  is  useful 
to  plants  in  summer,  but  not  in  winter.  There  are  two  general  types 
of  seasonal  rainfall  in  the  temperate  zones,  the  marine  or  winter 
type,  and  the  continental  or  summer  type.  In  general,  windward  coasts 
and  islands  have  the  former,  while  interiors  and  leeward  coasts  have 
the  latter. 

Both  the  variations  of  temperature  and  the  distribution  of  rain- 
fall have  far-reaching  effects  on  life,  some  of  which  may  be  pointed 
out.  Civilization,  which  apparently  began  near  the  tropics,  has 
moved  steadily  outward  (especially  northward),  until  its  chief  centers 
are  now  in  the  middle  latitudes  of  the  northern  hemisphere  (p.  114), 
where  the  seasons  are  commonly  regarded  as  responsible  for  much 
of  the  energy,  thrift,  and  industry  which  have  brought  about  this 
advanced  development.  The  change  of  seasons  stimulates  effort. 
In  summer,  the  conditions  of  life  in  many  parts  of  the  temperate 
zones  are  almost  as  easy  as  in  tropical  regions.  Summer  is  a  time  of 
abundance,  and  winter  a  time  of  scarcity,  in  nature's  supplies.  In 
summer,  it  is  necessary  to  provide  food,  clothing,  and  shelter  for  the 
winter,  when  nature  does  not  provide.     In  order  to  live,  therefore, 


SUB-TROPICAL   CLIMATE  117 

man  must  plan  for  the  future,  and  to  secure  the  things  he  needs 
requires  regular  effort;  but  with  planning  and  effort,  it  is  possible 
for  him  to  secure  what  he  needs.  These  conditions  lead  to  mental, 
physical,  and  industrial  development,  and  such  development  is  the 
basis  for  advance  in  civilization. 

South  temperate  zone.  The  limited  extent  of  land  in  the  south 
temperate  zone  gives  it  a  climate  far  less  variable  than  that  of  the 
corresponding  northern  zone. 

Types  of  Climate 

The  north  temperate  zone  is  a  patch-work  of  climatic  types, 
whether  the  division  is  based  on  temperature  or  on  rainfall.  The 
south  temperate  zone,  with  its  smaller  land  areas,  mostly  near  the 
sea,  has  few  important  types  of  climate. 

The  chief  types  of  climate  of  both  hemispheres  are  determined 
by  (i)  the  distribution  of  land  and  water,  (2)  winds,  and  (3)  altitude. 
With  insolation,  these  factors  control  both  temperature  and  rainfall. 
The  following  important  types  of  climate  are  recognized:  (i)  That 
of  windward  coasts  in  low  latitudes,  the  sub-tropical  type;  (2)  that  of 
windward  coasts  in  high  latitudes  (above  40°) ;  (3)  that  of  continental 
interiors,  a  type  which  varies  much,  especially  in  amount  of  rainfall; 
and  finally,  (4)  the  modifications,  particularly  of  (3),  brought  about 
by  altitude. 

I.      WINDWARD    COASTS    IN    LOW    (bELOW    40°)    LATITUDES 

General  characteristics.  The  chief  features  of  sub-tropical 
climates  are  moderate  temperatures,  with  small  annual  and  large 
diurnal  ranges.  In  these  respects  the  climate  resembles  that  of  the 
tropics.  The  rainfall  is  rather  light  in  most  places  (Fig.  39),  and 
is  greatest  in  winter.  The  summers  are  dry.  This  climate  is  typical- 
ly sunny,  with  a  maximum  of  cloudiness  in  winter. 

Distribution.  The  sub-tropical  type  of  climate  is  found  in 
latitudes  affected  alternately  by  the  trade-winds,  the  tropical  belts 
of  high  pressure,  and  the  westerly  winds.  It  is  developed  best  on 
islands  and  on  the  western  (windward)  coasts  of  continents  between 
the  parallels  of  about  25°  and  40°.  It  prevails  over  much  of  the 
land  of  the  south  temperate  zone  and  is  widespread  about  the  Mediter- 
ranean Sea,  extending  from  Spain  on  the  west  through  Italy  and  the 


ii8     TYPES  OF   CLIMATE  IN  TEMPERATE  ZONES 

southern  part  of  the  Balkan  Peninsula  into  western  Asia,  as  well  as 
across  the  northern  part  of  Africa.  The  wide  extent  of  the  sub- 
tropical climate  about  the  Mediterranean  has  led  to  the  name  "Med- 
iterranean climate."  In  North  America,  this  type  of  climate  is 
almost  confined  to  the  coastal  part  of  California,  south  of  San  Fran- 
cisco. The  climate  of  southern  California  may  be  taken  to  illustrate 
the  type. 

Southern  California 

The  southward  migration  of  the  wind  systems  in  winter  brings 
southern  California  under  the  influence  of  westerly  winds.  The 
northward  migration  of  the  wind  systems  in  summer  brings  it  in 
turn  under  the  influence  of  (i)  greatly  weakened  westerlies,  (2)  the 
tropical  high  pressure  belt,  and  (3)  the  northern  margin  of  the  trade- 
winds. 

Temperatures.  The  latitude  is  high  enough  to  prevent  a  long 
continuation  of  temperatures  as  high  as  those  of  the  tropics,  and 
nearness  to  the  sea  prevents  the  seasonal  extremes  characteristic 
of  most  places  in  the  temperate  zones.  Freezing  temperatures  are 
rare  in  low  altitudes.  Daily  ranges  of  temperature  are  greater  than 
yearly  ranges.  On  the  whole,  the  temperature  of  southern  California 
is  much  like  that  of  tropical  lands  at  moderate  altitudes. 

In  some  ways  the  sub-tropical  type  of  climate  is  the  best  in  the 
world,  and  is  described  frequently  as  being  like  "perpetual  spring." 
It  is  healthful,  as  shown  by  the  popularity  of  southern  California, 
where  Pasadena,  Riverside,  San  Diego,  and  other  cities  duplicate, 
on  a  small  scale,  the  noted  resorts  in  the  Riviera  of  southern  France 
and  Italy.  The  sunny  skies  (68  per  cent  for  San  Diego)  help  greatly 
to  make  these  places  popular,  especially  in  autumn,  winter,  and 
spring.  The  dry  season  (summer)  may  be  disagreeable  because  of 
(i)  the  heat,  (2)  the  drying  up  of  vegetation,  and  (3)  fogs  and  dust. 
Many  places  in  California  have  least  sunshine  in  the  dry  season  on 
account  of  fogs. 

The  absolute  lowest  temperature  at  San  Diego  is  32°,  and  the 
absolute  maximum  101°.  Such  variations  are  characteristic  of 
tropical  lands  where  the  average  annual  range  is  not  more  than  15° 
to  20°.  Interior  stations  show  greater  average  ranges  and  more 
marked  extremes,  because  they  are  farther  from  the  sea.  Their 
mean  maxima  are  higher,  their  mean  minima  are  lower,  and  the  fre- 
quency of  both  high  and  low  temperatures  is  much  greater. 


MARINE   CLIMATE  119 

Rainfall.  As  in  most  similar  localities  (Fig.  39)  the  precipita- 
tion in  southern  California  is  rather  low,  and  there  is  a  marked  winter 
maximum.  The  summers  are  almost  rainless  for  a  period  which 
varies  considerably  from  place  to  place.  The  interior  valley  of 
California  is  dry  at  all  times  because  the  coast  ranges  have  taken 
the  moisture  out  of  the  winds  from  the  ocean.  The  dryness  increases 
the  range  of  temperature  in  the  valley. 

Rainfall  and  Crops 

During  the  dry  season,  most  vegetation  dries  up  unless  irrigated. 
Where  water  is  available,  the  abundance  of  sunshine  and  the  favor- 
able temperatures  lead  to  extensive  irrigation,  as  in  southern  Califor- 
nia and  in  the  favored  parts  of  southern  Europe,  western  Asia,  and 
northern  Africa.  Most  of  the  crops  of  these  latitudes,  however,  are 
grown  during  the  rainy  winter  season  and  harvested  in  spring,  before, 
or  soon  after,  the  beginning  of  the  dry  season.  Winter  crops  are 
made  possible  by  the  temperatures  of  that  season.  Winter  wheat  is 
a  common  cereal  crop,  as  in  Italy,  southwestern  Australia,  and 
California,  while  barley,  resistant  to  both  heat  and  dryness,  was 
long  the  chief  cereal  in  such  climates.  Corn  cannot  be  grown  without 
irrigation,  for  it  needs  a  high  temperature  (such  as  that  of  the  dry 
season)  during  growth. 

The  characteristic  crop  of  the  sub-tropical  climate  is  fruit. 
Oranges,  lemons,  olives,  grapes,  and  other  fruits  are  produced 
abundantly  in  southern  California  and  in  Mediterranean  lands. 
There  is  possibility  of  frost,  however,  and  frost-fighting  is  an 
important  part  of  the  business  of  the  California  fruit  grower. 
In  many  sub-tropical  localities,  fruit-drying  is  an  important 
industry,  favored  by  the  dry,  sunny  weather  which  follows  the 
ripening  of  the  fruit. 


2.    WINDWARD  COASTS   IN   LATITUDES  ABOVE   40°;   MARINE  CLIMATE 

Location.  The  marine  type  of  climate  in  this  zone  is  controlled 
by  prevailing  westerly  winds,  blowing  almost  constantly  from  ocean 
to  land.  The  climate  is  cool,  damp,  and  rainy.  The  change  from 
the  sub-tropical  type  of  climate  is  gradual,  and  in  some  ways  the 
two  types  are  not  very  unlike. 

In  the  western  hemisphere,  this  type  of  climate  is  developed  best 
(i)  in  Chile,  south  of  latitude  40°  and  west  of  the  Andes  Mountains, 


I20     TYPES   OF   CLIMATE   IN  TEMPERATE  ZONES 

and  (2)  near  the  coast  from  San  Francisco  to  the  Arctic  Circle.  It 
is  modified  greatly  even  east  of  the  low  coast  ranges. 

In  the  eastern  hemisphere,  neither  Africa  nor  Australia  extends 
into  latitudes  high  enough  to  have  this  type  of  climate;  but  it  affects 
parts  of  Tasmania  and  most  of  New  Zealand.  It  affects  the  coast 
of  Europe  from  France  to  the  Arctic  Circle,  and  extends  far  inland 
because  there  is  no  continuous  north  and  south  mountain  range  to 
take  the  moisture  from  the  westerly  winds.  The  change  from 
marine  to  continental  conditions  here  is  very  gradual.  From  the 
British  Isles,  the  annual  rainfall  decreases  gradually  eastward,  the 
winter  maximum  gives  way  to  spring  and  summer  maxima,  and 
the  ranges  and  extremes  of  temperature  become  more  marked.  If 
the  marine  influence  did  not  reach  far  inland,  the  densely  populated 
and  highly  developed  countries  of  western  Europe,  especially  north 
of  latitude  50°,  would  be  far  less  important  than  now.  The  temper- 
ing effect  of  the  westerly  winds  on  the  climate  of  western  Europe  is 
increased  by  the  relatively  high  temperature  of  the  central  and 
eastern  parts  of  the  North  Atlantic  Ocean. 

Temperatures.  The  variations  of  temperature  are  less  than 
in  the  same  latitudes  elsewhere.  Thus  the  yearly  range  of  tempera- 
ture at  Sitka,  Alaska,  Lat.  57°,  is  only  25°,  hardly  more  than  that 
in  some  parts  of  the  tropics,  and  at  Thorshaven,  in  the  Faroe  Islands, 
Lat.  62°,  the  range  is  only  14.2°.  In  this  respect,  this  type  of  climate 
resembles  the  sub-tropical  type,  though  the  actual  temperatures  are 
lower  (Why?).  It  is  the  only  really  temperate  climate  of  the  inter- 
mediate zone. 

Regions  having  a  marine  climate  have  mild  winters  and  cool 
summers,  and  their  average  yearly  temperatures  are  higher  than 
those  of  other  regions  in  the  same  latitude.  For  example,  Ireland, 
which  represents  perhaps  the  extreme  case,  is  30°  or  40°  too  warm 
for  its  latitude,  55°  N. 

Rainfall  and  humidity.  Places  freely  exposed  to  westerly  winds 
get  much  rain  in  winter,  when  the  land  is  cooler  than  the  sea.  In 
summer,  low  lands  are  warmer  than  the  ocean  and  receive  little 
rain,  though  the  dry  season  is  much  shorter  than  in  lower  latitudes 
(Why?).  Mountainous  western  coasts  have  abundant  rainfall,  high 
humidity,  and  much  cloudiness  all  the  year.  In  some  places  fogs 
occur  almost  daily,  and  in  extreme  cases,  as  along  the  coast  of  Alaska, 
they  may  last  for  weeks  at  a  time.     Evaporation  is  extremely  low. 


MARINE   CLIMATE   AND   LIFE  121 

Though  the  maximum  precipitation  is  in  winter,  little  of  it  is  in  the 
form  of  snow,  except  at  high  altitudes. 

Effect  on  life.  Cool  summers,  abundant  moisture,  and  much 
cloudiness,  prohibit  the  growth  of  many  kinds  of  crops.  For  example, 
wheat  and  corn  are  not  grown  in  the  typical  marine  climate  of  western 
North  America  and  northwestern  Europe.  Wheat  requires  a  dry, 
sunny  harvest  season,  and  so  its  growth  near  the  coasts  in  question 
is  confined  to  places  where  topography  modifies  marine  conditions, 
as  in  eastern  Washington  and  eastern  England.  Corn  needs  a  higher 
temperature  and  more  sunshine  than  the  marine  climate  affords. 
Oats,  rye,  and  barley,  however,  are  grown  successfully  in  a  cool, 
cloudy,  damp  climate.  This  is  a  chief  reason  why  oats  have  fur- 
nished the  staple  food  of  Scotland.  Various  crops  are  grown  near 
the  northern  limit  of  the  intermediate  zone  in  northwestern  Europe 
and  in  Alaska.  In  Norway,  rye,  oats,  barley,  and  potatoes  are 
grown  successfully  within  the  Arctic  Circle.  In  Alaska,  barley, 
potatoes,  cabbages,  and  turnips  have  been  grown  at  Ft.  Yukon,  in 
latitude  66°  30'.  The  marine  climate  is  also  favorable  for  grass, 
which  in  some  places  grows  ten  or  eleven  months  in  the  year. 
For  this  reason,  the  raising  of  live  stock  is  or  may  be  important 
in  this  climate.  In  the  British  Isles,  for  example,  the  grazing  in- 
dustry has  long  been  the  leading  phase  of  agriculture.  Mild  tem- 
peratures and  abundant  moisture  make  Ireland  always  green  (Emer- 
ald Isle),  and  the  raising  of  cattle  is  a  chief  industry. 

Marine  climate  also  favors  the  growth  of  heavy  forests.  Good 
examples  of  such  forests  are  found  in  northwestern  United  States 
(p.  370),  where  lumbering  is  an  important  industry  and  forest  prod- 
ucts are  leading  articles  of  trade.  In  the  same  region,  mountains 
near  the  coast  cause  heavy  precipitation,  much  of  which  is  in  the 
form  of  snow.  The  melting  of  the  snow  in  summer  keeps  the  streams 
full  when  the  rainfall  is  least,  and  mountain  streams  afford  water 
power  (p.  290)  for  manufacturing.  Among  native  tribes,  forest 
conditions  lead  to  hunting  and  fishing  as  regular  pursuits. 

The  change  of  climatic  conditions  with  increasing  latitude  has  resulted  in 
striking  contrasts  in  man's  activities.  In  the  northern  part  of  Chile,  for  example, 
there  is  a  coastal  desert  at  the  margin  of  the  trade-wind  zone.  Here  conditions 
have  favored  the  accumulation  of  guano  and  nitrate  deposits,  which  have  been  the 
basis  of  important  industries  and  commerce,  and  the  cause  of  bitter  strife  between 
Chile  and  Peru.  South  of  the  desert,  the  sub-tropical  type  of  climate  has  led  to 
irrigation  and  the  growth  of  fruits.  Still  farther  south,  where  the  climate  is  of  the 
type  under  consideration,  grazing   and    the  raising  of  cereal  crops  and  vegetables 


122     TYPES   OF  CLIMATE  IN  TEMPERATE  ZONES 

are  the  chief  occupations.  In  the  extreme  southern  part,  the  heavy  rainfall  from 
the  westerly  winds  supports  luxuriant  forests,  and  forest  industries  and  fishing  are 
the  chief  occupations.  Similar  contrasts  exist  along  the  western  coast  of  North 
America  from  California  northward,  and  along  the  coast  of  Europe  from  Spain  to 
Norway. 

3    CONTINENTAL   CLIMATES 

Regions  affected.  This  type  of  climate,  as  its  name  implies, 
is  found  inland  from  windward  coasts ;  but  not  at  any  fixed  distance 
from  the  coast.  We  have  seen  already  that  the  marine  climate 
extends  far  from  the  western  coast  of  Europe  (p.  120),  and  but  a 
very  short  distance  from  the  west  coast  of  the  Americas  (p.  119). 

In  the  south  temperate  zone,  the  continental  climate  is  found 
only  in  southern  Argentina.  North  America  and  Eurasia,  on  the 
other  hand,  are  broad  in  rather  high  latitudes  (Fig.  58),  and  so  have 
continental  climates  over  wide  areas.  In  North  America,  there  is 
a  sharp  contrast  between  the  marine  climate  of  the  western  coast 
and  the  continental  climate  east  of  the  westernmost  high  mountains, 
the  continental  climate  affecting  most  of  the  United  States  and 
Canada.  In  Eurasia,  because  of  conditions  already  noted  (p.  120), 
the  marine  climate  of  western  Europe  grades  into  the  continental 
climate  which  affects  the  Russian  Empire  and  most  of  China. 

Temperatures.  The  chief  characteristic  of  the  continental 
climate  is  extremes  of  temperature.  These  extremes  are  due  largely  to 
the  fact  that  land  absorbs  and  radiates  heat  much  more  readily  than 
water  does.  The  winters  are  cold,  the  cold  increasing  (i)  with  the 
latitude,  and  (2)  with  increasing  distance  from  the  sea  to  windward. 
In  latitude  45°,  in  North  America,  the  lowest  temperatures  are 
about  —30°,  and  near  the  northern  Hmit  of  the  zone  they  reach  —60° 
or  even  less.  A  great  area  in  northeastern  Asia,  far  from  the  ocean 
to  windward,  has  extremely  low  temperatures  in  winter.  In  the 
United  States,  the  temperature  never  falls  to  —40°,  except  in  the 
extreme  northern  part  and  in  high  mountains,  and  there  but  rarely; 
but,  except  in  the  Gulf  region,  there  is  no  large  area  east  of  the 
Pacific  coast  where  temperatures  10°  to  20°  below  freezing  do  not 
occur  every  year.  The  summers  are  hot.  July  averages  of  60° 
are  found  even  beyond  the  northern  margin  of  the  zone,  and  maximum 
temperatures  of  80°  to  90°  are  found  close  to  the  Arctic  Circle.  In 
the  southern  part  of  the  zone,  the  summer  temperatures  are  tropical. 

The  annual  ranges  of  temperature  are  very  great,  especially 
in  the  northern  part  of  the  north  temperate  zone.    In  northwestern 


CONTINENTAL    CLIMATE  123 

Canada,  the  difference  between  the  lowest  and  the  highest  tempera- 
tures of  the  year  has  been  known  to  reach  150°,  and  in  northeastern 
Asia,  180°.  In  the  lower  latitudes  the  extremes  are  not  so  great; 
the  winters  are  milder,  and  the  summers  are  not  correspondingly- 
warmer.  In  our  southern  states  only  small  areas  ever  have  tempera- 
tures above  100°,  and  in  most  parts  of  the  zone  the  mean  maximum 
temperatures  are  under  90°,  or  no  higher  than  those  occasionally 
recorded  near  the  Arctic  Circle. 

Cyclonic  influence.  A  second  important  feature  of  continental 
climate  is  the  variability  of  weather  from  day  to  day.  Cyclones 
and  anticyclones  interrupt  the  prevailing  westerly  winds  frequently; 
hence  there  is  repeated  change  from  clear,  cold,  and  dry  days,  ta 
cloudy,  warm,  and  damp  ones.  Because  of  the  frequent  storms,  the 
winds  may,  in  the  course  of  a  day  or  two,  blow  from  all  points  of 
the  compass,  and  each  wind  tends  to  bring  its  own  distinctive  weather 
conditions.  The  northerly  winds  of  anticyclones  in  winter  carry 
freezing  temperatures  almost  to  the  southern  margin  of  the  zone. 
Southerly  winds,  on  the  other  hand,  carry  warm  air  to  comparatively 
high  latitudes,  and  temporarily  may  produce  a  summer-like  tem- 
perature in  mid-winter,  even  as  far  north  as  New  York  and  Chicago. 

Rainfall.  A  third  important  element  of  continental  climate 
is  its  rainfall,  which  is  very  variable,  but  as  a  rule  either  moderate 
or  scanty  (Figs.  39  and  59).  In  few  places  is  it  more  than  40  inches 
a  year,  and  most  of  it  comes  during  the  spring  and  summer.  The 
fact  that  most  rain  falls  when  temperatures  are  favorable  for  plant 
growth  is  most  important. 

Eurasia  illustrates  the  effect  on  rainfall  of  distance  from  the 
windward  coast.  The  western  slopes  of  the  British  Islands  have  So- 
to 100  inches  of  rain  yearly;  Germany  and  western  Russia  have  20 
to  30  inches;  eastern  Russia  and  western  Siberia,  between  15  and 
20  inches;  while  large  areas  of  central  and  eastern  Siberia  have 
less  than  10  inches. 

Arid  and  humid  interiors.  On  the  basis  of  rainfall,  there 
are  two  principal  subdivisions  of  continental  climate,  the  one  humid, 
and  the  other  arid.  These  types  merge  into  each  other  in  a  belt 
where  the  climate  is  semi-arid.  Forests  are  characteristic  of  the 
humid  cHmate,  but  they  give  place  to  grass  lands  where  the  climate 
is  semi-arid,  and  to  deserts  where  the  rainfall  is  very  slight.  In  a 
general  way,  moisture  decreases  with  increasing  distance  from  the 
ocean  to  windward;  but  topography  and  cyclonic  storms  modify  this 


124     TYPES   OF   CLIMATE   IN  TEMPERATE  ZONES 


CONTINENTAL   CLIMATES   IN   UNITED   STATES      125 

general  relation.  Altitude  also  is  an  important  factor  in  continental 
climate,  especially  in  arid  regions,  because  highlands  increase  precipi- 
tation. Lowland  deserts  may  give  place  to  grassy  lands  at  moderate 
altitudes,  and  to  forests  still  higher.  As  in  tropical  deserts,  the  effect 
of  high  elevations  plays  an  important  part  in  the  life  of  the  arid  regions. 

With  but  slight  modification,  the  continental  climates  extend 
eastward  to  the  oceans.  Ranges  of  temperature  are  somewhat  less 
near  the  eastern  seaboard,  and  the  rainfall  is  somewhat  greater 
(Fig.  39)- 

Continental  Climates  in  the  United  States 

The  interior  of  our  country  may  be  divided  into  (i)  the  arid 
region  (Fig.  60),  chiefly  between  the  Sierra  Nevada  and  Cascade 
mountains  on  the  west  and  the  Rocky  Mountains  on  the  east;    (2) 


Fig.  60.     Map  showing  arid,  semi-arid,  and  humid  regions  of  the  United 
States.     (After  Newell.) 


the  semi-arid  region  between  the  Rocky  Mountains  and  longitude 
98°  to  100°;  and  (3)  the  humid  tract,  lying  farther  east.  All  these 
regions  have  extremes  of  heat  and  cold.  They  also  have  great  changes 
of  temperature  and  humidity  from  day  to  day  as  a  result  of  passing 
cyclones  and  anticyclones.  The  difference  in  the  amount  of  rainfall, 
however,  makes  the  conditions  of  life  very  different  in  the  three 
regions. 


126     TYPES  OF   CLIMATE  IN  TEMPERATE  ZONES 

(7)  The  Arid  Region 

The  arid  region  (Fig.  60)  includes  most  of  the  Cordilleran  section 
of  the  United  States,  except  the  high  mountains.  Its  western  margin 
is  near  the  western  coast,  because  the  mountains  there  stop  much 
moisture  which  otherwise  would  be  carried  inland  by  the  westerly 
winds.  The  average  annual  rainfall  in  the  arid  belt  is  less  than  15 
inches,  and  over  large  areas,  less  than  10  inches  (Fig.  59).  Sunshine 
prevails  throughout  the  year,  relative  humidity  is  low,  and  evapora- 
tion high.  The  nights  are  usually  cool  even  when  the  days  are  hot. 
The  heat  of  summer  is  great,  but  the  humidity  is  so  low  that  the 
sensible  temperatures  are  not  very  high.  So  far  as  comfort  is  con- 
cerned, the  arid  region  has  an  agreeable  temperature. 

Effects  of  scanty  rainfall.  The  scanty  rainfall  means  scanty 
vegetation,  except  where  high  elevations  cause  rain  enough  to  support 
grass  or  timber.  The  rapid  evaporation  of  ground-water  leaves  the 
alkaline  substances  it  contains  in  the  soil,  and  the  slight  rains  are 
not  enough  to  dissolve  and  carry  these  away.  In  some  places  this 
gives  rise  to  alkaline  soils,  unfavorable  for  vegetation.  Where  not 
alkaline,  desert  soils  are  naturally  rich,  because  elements  important 
for  plant  food  have  not  been  leached  out  or  used  up  (p.  293).  Hence 
where  water  can  be  applied  to  desert  lands,  they  are  highly  productive 
in  most  cases. 

Many  mountains  in  the  arid  region  receive  much  snow  in  winter, 
and  this  may  afford  water  for  irrigation.  The  total  area  which  can 
be  irrigated,  however,  is  but  a  small  portion  of  the  entire  arid  tract 
(p.  293).  Farming  is  therefore  not  the  leading  industry  of  arid 
lands.  Where  rainfall  is  enough  to  support  even  a  meager  growth 
of  grasses,  grazing  is  an  important  occupation. 

Mining  is  important  in  parts  of  the  arid  West,  though  aridity  has 
little  or  nothing  to  do  with  the  development  of  ores.  Desert  condi- 
tions favor  the  accumulation  of  salt  deposits,  as  about  Salt  Lake, 
and  borax  deposits,  as  in  Death  Valley,  California. 

The  population  of  the  arid  section  is  necessarily  scanty,  because 
there  is  no  natural  basis  for  permanent  or  extensive  settlement  in 
most  localities. 

(2)   The  Semi- Arid  Region 
In  the  semi-arid  region  (Fig.  60),  the  yearly  rainfall  is  between 
15  and  20  inches  (Fig.  59),  most  of  which  falls  in  spring  and  summer. 


CONTINENTAL  CLIMATES   IN   UNITED    STATES      127 

The  tract  is  without  high  mountains,  so  that  there  is  Httle  increase 
of  precipitation  as  the  result  of  altitude,  and  forests  are  generally 
absent.  The  region  is  sunny,  and  the  temperatures  are  high  in 
summer  and  low  in  winter.  The  sensible  effects  of  the  extremes, 
however,  are  moderated  by  the  dryness  of  the  air.  The  open  charac- 
ter of  the  country  favors  free  circulation  of  the  atmosphere,  and 
fairly  constant  winds  of  moderate  to  high  velocity  are  more  or  less 
typical  of  most  of  the  region. 

Effect  on  life.  The  semi-arid  district  is  a  region  of  grass  land; 
there  is  not  enough  rain  for  most  cultivated  crops.  Grazing  conse- 
quently has  been  the  most  general  occupation.  Water  is  highly 
prized,  and  bitter  contests  have  been  waged  over  the  question  of  its 
ownership.  Thus  the  use  of  the  waters  of  the  Arkansas  River,  which 
flows  from  Colorado  into  Kansas,  led  to  a  long  legal  battle  between  the 
two  states,  because  there  was  not  water  enough  for  both. 

(3)    The  Humid  Region 

The  semi-arid  region  merges  gradually  into  the  humid  region 
farther  east  (Fig.  60).  The  temperatures  of  the  two  regions  are  not 
unlike,  but  in  the  humid  region  cloudiness  and  humidity  are  greater, 
and  evaporation  less;  hence  sensible  temperatures  are  higher  irr 
summer  and  lower  in  winter.  The  precipitation  rarely  falls  so  low 
as  20  inches  per  year,  and  most  of  it  comes  in  summer.  The  amount 
of  rain  necessary  for  crops  without  irrigation  varies  with  the  latitude. 
More  is  needed  in  Oklahoma  than  in  Dakota,  because  the  higher 
temperature  and  lower  humidity  of  the  former  cause  greater  evapora- 
tion. In  the  western  part  of  this  region,  trees  grow  in  the  river 
bottoms;  farther  east,  they  become  more  abundant,  and  forests  are 
found  (or  were  once)  over  large  areas.  Throughout  the  humid  region 
there  is  rain  enough  for  cultivated  crops,  and  it  contains  some  of  the 
greatest  agricultural  tracts  of  the  temperate  zones. 

Effects  on  life.  The  crops  raised  are  determined  largely  by 
the  climate.  Wheat,  for  example,  is  raised  most  in  the  less  rainy 
regions  (Fig.  260),  and  its  seed  time  and  harvest  are  influenced  by 
climate.  In  the  north,  spring  wheat  is  grown,  largely  because  the 
winters  are  too  cold  for  wheat  sown  in  the  autumn.  Farther  south, 
where  the  winter  season  is  shorter  and  milder,  both  winter  and  spring 
wheat  may  be  grown,  the  former  predominating  in  many  sections. 
The  harvesting  of  winter  wheat  begins  in  the  south  in  June,  and 
the  harvesting  of  spring  wheat  ends  in  the  north  about  the  first  of 


128     TYPES   OF   CLIMATE   IN  TEMPERATE  ZONES 

September.  The  harder  varieties  of  wheat,  rich  in  gluten  and  good 
for  macaroni,  are  grown  in  the  drier  sections  (p.  360),  while  softer 
varieties,  less  rich  in  gluten,  but  good  for  flour,  are  grown  where 
rain  is  more  plentiful. 

The  best  climate  for  wheat  is  one  with  a  dry,  sunny  harvest  season, 
such  as  that  of  the  Sacramento  Valley,  California,  and  eastern  Wash- 
ington (p.  121).  This  ideal  climate  is  not  found  in  much  of  the 
humid  interior,  where  wheat  is  the  standard  crop  only  in  a  north- 
south  belt,  some  ten  degrees  in  width,  just  east  of  the  looth  meridian. 
Even  here,  the  climate  is  not  so  good  for  wheat  as  that  of  eastern 
Washington. 

East  of  the  wheat  belt,  the  heavier  rains  favor  a  variety  of  crops. 
Corn  is  the  standard  cereal  in  great  areas  (Fig.  259),  though  wheat, 
oats,  and  other  crops  are  commonly  grown  in  rotation  with  it.  Corn 
is  not  grown  so  far  north  as  wheat,  because  corn  requires  a  higher 
temperature,  and  most  varieties  require  a  longer  warm  season.  With 
corn,  many  other  cereals,  vegetables,  and  fruits  are  grown,  requiring 
more  moisture  than  wheat. 

The  humid  continental  region  is  the  region  of  greatest  develop- 
ment in  the  United  States.  It  has  the  major  part  of  the  population 
(Fig.  281),  it  contains  most  of  the  chief  cities  (p.  399),  its  manufactur- 
ing and  commercial  activities  are  greatest  (p.  383),  and  its  transpor- 
tation facilities  are  best  (Fig.  279).  All  these  things  reflect  the 
abundant  yield  of  the  soil,  and  this  is  a  result,  in  large  part,  of  favor- 
able climate. 

The  abundance  of  rain  and  the  topography  of  the  eastern  coast 
of  the  United  States  favor  the  development  of  swamps,  and  in  low 
latitudes  swamps  invite  diseases  like  those  of  equatorial  regions 
(p.  103).  The  home  of  malaria  in  the  United  States  is  on  the  low 
plains  and  in  the  river  valleys  along  the  eastern  coast  south  of  New 
York.  Yellow  fever  has  been  introduced  many  times  into  the 
Gulf  and  South  Atlantic  ports,  but  could  not  last  from  one  summer 
to  the  next,  on  account  of  the  frosts  of  winter. 

Shore  towns  in  nearly  all  latitudes  feel  the  beneficial  effects  of  the 
sea-breeze  (p.  74),  and  many  important  seashore  resorts  from 
New  Jersey  northward  are  the  result.  In  the  higher  latitudes,  the 
ocean  affects  the  temperature  of  coastal  lands  chiefly  by  lowering 
the  temperature  in  summer,  because  of  frequent  winds  (sea-breezes 
and  cyclonic  winds)  from  the  east.  The  July  mean  for  Labrador, 
for  example,  is  13°  or  14°  lower  than  that  for  Norway  House,  at  the 


IMPORTANCE  OF  HUMID   REGIONS  129 

northern  end  of  Lake  Winnipeg,  near  the  great  Canadian  wheat 
district.  In  Labrador  none  of  the  cereals  will  ripen.  The  sparse 
population  there  finds  its  chief  support  in  fishing,  hunting,  and 
trapping.  Fishing  especially  is  important  during  the  summer,  and 
when  the  catch  is  small,  the  people  suffer  greatly  from  want  during  the 
long,  cold  winter. 

The  same  factors  which  lower  the  temperature  and  increase  the 
rainfall  along  our  eastern  coast  increase  cloudiness  and  fog.  Places 
exposed  freely  to  the  sea  (like  Newfoundland)  have  conditions  of 
humidity,  cloudiness,  and  fog  similar  to  those  of  marine  climates  on 
western  coasts.  Along  the  eastern  coast,  therefore,  the  continental 
climate  is  somewhat  modified. 

The  humid  parts  of  the  north  temperate  zone  are  the  greatest 
cereal  districts  of  the  world.  They  bear  the  same  relation  to  the  cul- 
tivation of  cereals  that  the  semi-arid  steppe  lands,  with  their  grassy  veg- 
etation, hold  to  the  live  stock  industry  of  the  world.  Thus  the  great 
wheat  regions  lie  mainly  between  the  40th  and  55th  parallels.  Rye, 
closely  related  to  wheat  in  its  uses  and  conditions  of  growth,  replaces 
wheat  in  many  places  where  the  soils  are  too  poor  for  the  latter. 
Of  the  other  great  cereal  crops  in  this  belt,  oats  and  barley  are  grown 
more  to  the  north,  and  corn  to  the  south.  Hence,  through  the  heart 
of  the  temperate  zone  is  found  the  home  of  all  the  cereals,  save  rice, 
which  serve  as  food  for  man.  This  arrangement  of  important  crops 
influences  both  the  distribution  of  population  and  the  movement  of 
commerce.  The  populous  part  of  the  temperate  zone  corresponds 
closely  to  the  cereal  belt.  Much  of  the  commerce  of  the  world  now 
moves  along  east  and  west  routes  in  these  same  latitudes.  No  other 
country  is  situated  so  well  as  the  United  States  with  respect  to 
cereal  growing  lands. 

The  whole  humid  section  in  the  interior  of  this  country  is  exposed 
to  sudden  frost  in  late  spring  and  early  autumn  (Fig.  61),  and  in 
either  case  widespread  damage  may  result.  Its  southwestern  part 
is  exposed  to  hot  winds  from  the  south  which,  in  exceptional  cases, 
wither  and  kill  crops.  Droughts  are  common,  though  less  frequent 
and  less  widespread  than  in  monsoon  countries.  Almost  every 
year  some  part  of  the  humid  portion  of  the  United  States  suffers 
from  too  little  rain;  but  severe  drought  rarely  affects  a  great  area, 
or  the  same  area  frequently.  In  monsoon  countries  like  India,  on 
the  other  hand,  a  large  area  suffers  from  drought  at  the  same  time, 
and  the  same  area  may  suffer  for  a  period  of  years.    Tropical  and  sub- 


I30     TYPES   OF   CLIMATE   IN  TEMPERATE  ZONES 

tropical  Australia  also  has  frequent  and  long-continued  droughts  which 
affect  large  areas.  In  spite  of  its  extremes  of  climate,  central  and 
eastern  United  States  is  a  highly  favored  agricultural  region,  largely 
because  of  its  reliable  rainfall. 

Near  the  northern  limit  of  the  north  temperate  zone  the  summers 
of  interior  lands  are  too  short  and  too  cold  for  cereals.  Even  in  the 
most  favored  parts  of  continental  interiors,  the  hardiest  cereals  cannot 


Fig.  6i.  Map  of  United  States  showing  average  dates  of  last  killing  frost  in 
spring  (broken  lines)  and  first  killing  frost  in  autumn  (solid  lines).  (After  U.  S. 
Weather  Bureau.) 

be  grown  much  beyond  the  6oth  parallel  (Fig.  58).  Dense  forests 
disappear  in  most  places  before  the  margin  of  the  zone  is  reached, 
being  replaced  by  the  scattered  trees  and  scanty  vegetation  which 
mark  the  beginning  of  the  frozen,  polar  wastes.  Both  Canada  and 
Russia  have  large  areas  of  this  nearly  worthless,  almost  uninhabited 
territory  (p.  336).  The  United  States,  on  the  other  hand,  is  neither 
too  far  north  nor  too  near  the  equator.  Climatically,  it  has  the  best 
position  of  any  large  country. 


4.      MOUNTAIN  CLIMATES 

Temperature.     Even  moderate  altitudes  so  affect  temperature 
as  to  determine  what  crops  may  be  cultivated.     For  example,  in 


MOUNTAIN   CLIMATE  131 

the  plateau  sections  of  Pennsylvania,  in  latitude  40°  to  42°,  corn  can- 
not be  depended  on  to  ripen  at  an  altitude  of  2,000  feet.  In  some  of 
the  drier,  hence  warmer  (in  summer)  and  sunnier,  parts  of  the  arid 
West,  corn,  under  irrigation,  will  ripen  at  much  higher  altitudes 
(4,000  feet  about  Great  Salt  Lake).  In  general,  the  upper  limit  for 
even  the  hardiest  crops  does  not  exceed  6,000  feet,  even  in  the  lower 
latitudes  of  the  temperate  zone.  In  contrast,  corn  is  grown  in 
Bolivia  at  an  altitude  of  10,000  feet,  and  wheat  even  higher.  The 
timber-line  (upper  limit  of  timber)  in  the  United  States  ranges  from 
an  altitude  of  about  11,000  feet  at  the  south,  to  7,000  or  8,000  at  the 
north,  and  the  level  at  which  snow  lies  most  of  the  time  is  not  far  above 
these  limits.  Hence,  so  far  as  agriculture  is  concerned,  the  higher 
lands  of  the  temperate  zone  are  of  little  use. 

Precipitation.  The  effect  of  altitude  on  rainfall  is  the  same 
in  the  temperate  zone  as  elsewhere.  It  increases  the  amount  of 
precipitation,  and  tends  in  many  cases  toward  a  maximum  in  winter. 
The  increased  precipitation  at  higher  altitudes  usually  results  in 
heavy  snowfall  in  winter.  Thus  Baltimore,  altitude  104  feet,  has 
an  average  of  23.8  inches  of  snow  annually,  while  Grantsville,  Md., 
altitude  3,400  feet,  has  71.2  inches.  Summit,  the  top  of  the  pass 
(7,017  feet)  crossed  by  the  Southern  Pacific  railroad  east  of  Sacra- 
mento, Cal.,  has  an  average  snowfall  of  433  inches  a  year,  and  twice 
in  thirty-three  years  the  amount  has  reached  775  inches.  Sacramento, 
on  low  land  to  the  west,  has  only  a  trace  of  snow  each  year. 

Winter  snowfall  is  an  important  factor  in  the  flow  of  many  rivers. 
Disastrous  winter  and  spring  floods  are  the  result  in  some  cases 
(p.  76),  and  in  others  the  supply  of  water  from  melting  snow  is  an 
important  aid  in  (i)  the  development  of  water  power,  (2)  the  main- 
tenance of  a  sufficient  depth  of  water  for  navigation,  and  (3)  irrigation. 
Heavy  winter  snows  and  snowslides  offer  serious  problems  to  railroad 
lines  which  run  at  high  levels,  and  at  the  bases  of  mountains.  Snow- 
slides  are  one  of  the  things  to  be  feared  about  mines  in  mountains, 
and  mountain  villages  have  been  destroyed  by  them. 

Mountain  conditions  of  temperature  and  rainfall  favor  forests, 
and  make  many  mountains  the  sites  of  lumbering  (p.  316).  Forest 
trees  thrive  far  above  the  altitudes  which  limit  crops.  Even  in 
arid  regions,  some  areas  5,000  to  6,000  feet  high  have  rain  enough 
to  support  forests  of  commercial  value. 

Many  mountains  serve  as  health  and  pleasure  resorts  (p.  317). 
Most  mountain  health  resorts  are  visited  chiefly  by  persons  afflicted 


132     TYPES   OF   CLIMATE   IX  TEMPER.\TE   ZONES 

with  diseases  of  the  lungs,  especially  tuberculosis.  Mountain  climate 
is  not  a  cure  for  this  disease;  but  the  conditions  in  the  mountains 
may  aid  in  checking  it,  or  may  even  enable  the  organs  affected  to 
throw  it  off.  The  favorable  conditions  are  (i)  the  pure,  dry  air  char- 
acteristic of  the  higher  altitudes  of  many  mountains,  and  (2)  the  de- 
creased density  of  the  atmosphere,  which  stimulates  the  lungs  to 
greater  activity.  In  the  arid  parts  of  western  United  States,  these 
conditions  are  associated  with  bright,  sunny  weather,  which  favors 
out-of-door  life. 

Questions 

1 .  Explain  the  absence  of  summer  rainfall  in  sub-tropical  climates,  even  with 
winds  from  the  ocean. 

2.  Account  for  the  morning  fogs  of  the  coast  of  southern  California  in  summer. 

3.  WTiy  is  the  Pacific  Ocean  not  the  chief  source  of  moisture  for  the  United 
States? 

4.  Explain  the  differences  in  climatic  conditions  at  different  points  on  the 
41st  parallel  in  the  United  States.     Along  the  32nd  parallel. 

5.  Explain  the  increase  in  rainfall  from  San  Diego  northward  to  Astoria. 
(See  Fig.  59  and  Plate  II.) 

6.  WTiy  are  the  limits  of  cereals  and  of  permanent  habitations  nearer  the 
equator  in  Fig.  57  than  in  Fig.  58? 

7.  How  does  the  isotherm  of  50°  in  Fig.  57  differ  from  that  of  Fig.  58?     Why? 

8.  Why  do  the  lines  showing  average  dates  of  frost  (Fig.  61)  turn  northward 
over  Lake  Erie  and  along  the  south  Atlantic  coast? 

9.  Why  is  the  snowfall  in  the  Mississippi  Valley  heavier  than  that  in  the 
corresponding  latitudes  on  the  Atlantic  coast? 

10.    Suggest  reasons,  based  on  climate,  why  there  is  little  commerce  between 
lands  of  the  south   temperate  zone. 


CHAPTER  XI 
CLIMATE   OF   POLAR   REGIONS 

General  Considerations 

Extent  of  polar  regions.  The  limits  of  the  polar  regions  are 
commonly  placed  at  the  Arctic  and  Antarctic  circles;  but  they  are 
sometimes  regarded  as  being  limited  equatom-ard  by  the  isotherm  of 
50°  for  the  warmest  month,  an  isotherm  which  marks  the  approxi- 
mate limit  of  the  growth  of  trees  and  cereals  (Fig.  62).  In  this  dis- 
cussion, the  latitude  division  is  used.  Thus  defined,  the  polar  regions 
have  an  area  about  one-twelfth  that  of  the  earth. 

General  features  of  polar  climate.  All  polar  regions  are  alike 
in  ha\-ing  the  sun  above  the  horizon  for  more  than  twenty-four  con- 
secutive hours,  and  below  the  horizon  for  a  similar  period,  once 
each  year.  Near  the  margins  of  these  zones,  the  longest  period  of 
continuous  sun  is  only  a  few  days  (of  24  hours  each) ;  but  the  time 
during  which  the  sun  does  not  set  increases  poleward,  and  at  the 
poles  the  day  (period  of  continuous  light)  is  six  months  long  (p.  43). 
During  the  period  of  continuous  light,  insolation  is  greater  in  polar 
regions  than  in  low  latitudes  (p.  35),  but  the  temperature  of  the  lower 
air  is  not  raised  accordingly,  because  (i )  the  sun 's  rays  are  very  oblique 
(Fig.  21),  and  (2)  much  of  the  heat  which  reaches  the  surface  melts 
ice  and  snow,  and  is  not  effective  in  warming  the  air.  The  result  is  a 
low  temperature  for  the  year,  and,  except  for  lands  free  from  snow  and 
ice,  a  low  temperature  at  all  times  of  the  year. 

Temperatvire.  Many  of  the  recorded  temperatures  of  January 
in  the  Arctic  region  range  from  —  40°  to  —  60°,  while  the  warmest 
month  has  an  average  temperature  of  ^2°  or  more  in  many  places. 
The  maximum  summer  temperatures  close  to  the  margin  of  the  zone 
are  locally  as  high  as  80°,  or  even  90°;  but  such  temperatures  occur 
only  where  there  are  large  areas  of  land  free  from  snow  and  ice.  Most 
of  the  Antarctic  region  has  a  summer  temperature  below  the  freezing 
pomt  even  during  the  warmest  month,  so  far  as  present  records  show. 

The  annual  range  of  temperature  in  the  Arctic  region  is  greater 

133 


134 


CLIMATE  OF  POLAR  REGIONS 


than  that  in  the  Antarctic,  because  more  land  in  the  former  is  without 
snow  and  ice  in  summer.  Verhoyansk,  in  Siberia,  just  within  the 
Arctic  Circle  (Lat.  67°  6'),  has  a  July  mean  of  +60°  and  a  January 


Fig.  62.     Map  of  North  Polar  Zone,  showing  land  and  water  areas.     Pole- 
ward limit  of  growth  of  cereals Poleward  limit  of  growth  of  forest  trees 

.    Poleward  limit  of  permanent  habitations  +  +  +  +  +.   Isotherm  of  50°  for 

warmest  month . 


mean  of  —  60°.  In  contrast,  Hammerfest  (Lat.  70°  40'),  on  the 
coast  of  Norway,  and  the  most  northerly  town  in  Europe,  has  a  Janu- 
ary mean  of  23°,  and  a  July  mean  of  53°.  Hammerfest  shows  the  full 
effect  of  the  ocean  on  the  temperature  of  windward  coasts  in  high 
latitudes. 


THE  LIFE  OF  ANTARCTIC  REGIONS  135 

Humidity  arid  precipitation.  The  low  temperatures  aflfect  the 
other  elements  of  climate.  They  mean  little  evaporation,  and  hence 
little  moisture  in  the  air.  The  relative  humidity  varies  from  extreme- 
ly low,  especially  far  from  the  sea  to  windward,  to  relatively  high, 
particularly  on  windward  coasts.  The  precipitation  is  light,  prob- 
ably averaging  less  than  15  inches  a  year  except  on  windward  coasts. 

The  Shackleton  expedition  to  Antarctica  found,  from  recording  instruments 
left  by  a  preceding  expedition,  that  the  average  precipitation  for  six  years  had  been 
the  equivalent  of  7  to  8  inches  of  rain.  Most  of  the  precipitation  in  polar  regions 
is  in  the  form  of  snow,  and  is  frequently  accompanied  by  violent  winds.  Rain  is 
said  to  fall  in  most  parts  of  the  north  polar  region  during  the  warmer  months.  In 
the  south  polar  region  the  Shackleton  expedition  found  all  precipitation  during  13 
months  to  be  in  the  form  of  snow. 

The  great  fields  of  snow  and  ice  in  the  polar  regions  are  not  due 
to  heavy  snowfall,  but  to  the  preservation  of  most  of  that  which  falls. 

In  summer,  fogs  are  common,  and  are  a  great  hindrance  to  navi- 
gators. 

The  Antarctic  Region 

The  Antarctic  region  is  largely  ice-covered  water  and  ice-covered 
land.  The  scattered  land  areas  which  have  been  discovered  are 
probably  parts  of  an  Antarctic  continent.  Beyond  the  edge  of  this 
ice-covered  land  the  surface  rises  toward  the  interior  to  heights  of 
several  thousand  feet. 

If  the  south  polar  region  were  limited  by  the  isotherm  of  50°  for 
the  warmest  month,  it  would  include  everything  south  of  the  55th 
parallel. 

Temperature.  The  great  expanses  of  ice  and  ice-water  do  not 
allow  the  temperature  of  this  zone  to  rise  much  above  32°,  even  in 
summer.  During  this  season,  fog  and  cloud  are  so  frequent  that  much 
insolation  is  cut  off.  Fogs  and  clouds  are  therefore  important  factors 
in  keeping  the  summer  temperatures  low. 

The  mid-winter  (July)  temperatures  of  the  lower  latitudes  of  this 
zone  are  about  — 15°  to  — 20°,  so  far  as  recorded.  The  temperatures 
of  higher  latitudes  are  probably  much  lower.  The  seasons  between 
winter  and  summer  are  very  short.  The  one  shows  a  rapid  rise  from 
the  low  temperatures  of  winter,  and  the  other  a  rapid  drop  from  the 
temperatures  of  summer. 

Effects  on  life.  The  Antarctic  region  is  without  most  kinds  of 
vegetation  familiar  to  us.     Some  mosses  and  lichens  are  found  on  such 


156  CLIMATE  OF  POLAR   REGIONS 

lands  as  are  free  from  ice  for  a  part  of  the  year,  but  no  form  of  vegeta- 
tion useful  to  man  is  known.  The  animal  life  is  mainly  marine,  whales 
and  seals  being  characteristic.  The  waters  abound  in  lowxr  forms  of 
life,  such  as  molluscs  and  still  simpler  types.  On  land,  animal  life  is 
represented  by  a  few  species  of  birds  and  insects.  Great  rookeries  of 
penguins  form  one  of  the  most  remarkable  assemblages  of  bird  life  to 
be  found  anywhere.  The  albatross,  gull,  and  some  other  kinds  of 
sea-coast  birds  also  are  found.  From  the  standpoint  of  life  in  general, 
however,  the  Antarctic  lands  are  as  close  an  approach  as  there  is  to 
an  absolute  desert. 

The  Arctic  Regions 

In  the  higher  latitudes  the  Arctic  Ocean  is  covered  with  ice  most 
of  the  year,  though  the  ice  is  more  or  less  broken  in  summer.  In 
the  lower  latitudes  much  of  the  ocean  is  free  from  ice  all  or  part  of  the 
time.  Snow  and  ice  cover  all  but  the  fringe  of  Greenland,  and  the 
larger  part  of  many  other  islands.  The  Arctic  portions  of  the  conti- 
nents are  not  covered  by  ice  and  snow  during  the  summer,  and  their 
climate  is  in  sharp  contrast  (How?)  with  that  of  regions  which  are  so 
covered.  There  is  also  a  great  contrast  between  the  interior  lands 
which  are  snow-free  during  the  summer,  and  windward  coasts,  such 
as  western  Alaska  and  northwestern  Norway,  which  are  affected  by 
the  moderating  influence  of  winds  from  the  oceans  (p.  134). 

Temperature.  The  temperatures  of  this  zone  vary  widely. 
The  lowest  yearly  temperatures  are  found  where  there  is  a  permanent 
covering  of  ice.  Such  observations  as  are  recorded  indicate  a  January 
mean  of  about  — 40*^  for  northern  Greenland,  while  its  July  mean 
is  near  the  melting  point.  The  continental  interior  of  Siberia  is 
even  colder  than  Greenland  in  winter.  In  summer,  however,  this 
same  region,  being  without  snow  or  ice,  becomes  very  much  warmer 
than  Greenland. 

Arctic  lands  free  from  snow  in  summer  have  great  extremes  of 
temperature,  and  summer  maxima  of  60°  to  80°  are  almost  typical 
of  the  margin  of  the  zone.  Temperatures  of  90°  or  more  are  reported 
frequently  from  Alaska  and  Siberia.  An  extreme  range  of  150°  for 
the  year  is  common,  and  the  highest  summer  and  lowest  winter  tem- 
peratures recorded  are  more  than  180°  apart. 

The  extreme  and  long-continued  cold  of  winter  is  sufficient  to  freeze 
the  water  in  the  ground  to  the  depth  of  scores  of  feet,  and  the  tempera- 
tures of  summer  suffice  to  melt  the  ice  in  the  top  part  only  of  the  soil. 


LIFE  IN  ARCTIC  REGIONS  137 

Plant  life.  The  relatively  high  temperatures  which  prevail  on 
ice-free  land  in  summer  permit  the  growth  of  many  kinds  of  plants. 
As  compared  with  the  temperate  zone,  however,  the  amount  ^nd 
variety  of  vegetation  are  meager.  Stunted  trees  of  the  hardier 
types,  such  as  larches,  pines,  birches,  and  willows,  grow  near  the  border 
of  the  Arctic  zone  (Fig.  62).  The  northern  limit  of  these  trees  is  near 
the  70th  parallel  in  Siberia  and  northwestern  Canada.  Dwarf  willows 
and  birches  (hardly  trees)  are  said  to  occur  8°  or  10°  farther  north. 
Mosses,  lichens,  and  other  low  types  of  plants  abound  in  the  Arctic 
tundra,  which  becomes  a  sea  of  mud  as  it  thaws  out  during  the  sum- 
mer. In  the  dry  places  in  the  tundra,  and  on  southerly  slopes  where 
drainage  of  the  soil  is  good  and  where  insolation  is  great,  there  are 
many  flowering  plants,  some  of  which  produce  berries.  On  the  west 
coast  of  Greenland,  poppies  grow  north  at  least  to  latitude  78°.  The 
plants  of  these  high  latitudes  are  rapid  growers,  as  the  short  growing 
season  would  let  no  other  plants  mature. 

The  temperatures  of  air  and  soil  exclude  crops  from  nearly  all  the 
polar  region.  There  are  a  few  localities,  as  in  northern  Norway  and 
favored  spots  in  Alaska  and  Siberia,  where  hardy  cereals  and  some 
vegetables  may  be  grown  (Fig.  62). 

Animal  life.  Animals,  as  well  as  plants,  are  more  abundant 
m  the  Arctic  regions  than  in  the  Antarctic.  Sea  life  is  more  abundant 
than  land  life.  The  larger  sea  animals  are  similar  to  those  of  the 
Antarct'c.  and  include  whales,  seals,  and  walruses.  All  these  animals 
are  important  to  the  people  living  in  the  Arctic  region,  and  are  the 
basis  for  certain  industries  carried  on  from  places  in  lower  latitudes. 
Thus,  sealing  and  whale  fishing  are  carried  on  close  to  the  Arctic  Cir- 
cle, and  even  within  it.  The  Arctic  seas  also  teem  with  smaller  forms 
of  life,  such  as  molluscs  and  small  crustaceans.  Birds  are  prominent 
in  the  summer.  The  little  auk,  dovekies,  guillemots,  and  (locally) 
the  eider  duck  abound.  Among  land  mammals,  the  reindeer,  fox, 
hare,  polar  bear,  and  musk-ox  may  be  mentioned. 

Arctic  people.  The  Arctic  region,  unlike  the  Antarctic,  is  in- 
habited by  human  beings,  the  best  known  of  whom  are  the  Eskimos 
(Fig.  62).  The  population,  however,  is  scanty,  scattered,  and,  on  the 
whole,  not  highly  civilized.  Along  the  southern  margin  of  the  zone, 
there  are  many  small  groups  of  people.  Farther  north,  the  groups 
are  fewer  and  smaller,  and  more  confined  to  coasts.  The  most 
northerly  permanent  settlements  are  on  the  west  coast  of  Greenland, 
the  northernmost,  Etah,  being  above  the  78th  parallel. 


138  CLIMATE   OF  POLAR   REGIONS 

For  all  inhabitants  of  polar  regions,  life  is  a  constant  struggle. 
The  cold  means  poverty  of  resources,  a  constant  fight  for  food  and 
clothing,  and  consequent  inability  to  progress.  Edible  plants  are 
absent,  except  in  the  lower  latitudes  of  the  zone,  and  for  a  short  time 
each  year.  Land  animals,  like  the  reindeer,  are  comparatively  scarce 
on  account  of  the  meager  vegetation.  Hence  the  people  depend  in 
large  part  on  marine  life,  and  most  of  them  live  along  the  coasts. 

Meat  is  the  principal  food,  and  is  furnished  by  the  seal,  the  walrus, 
and  fish,  supplemented  by  the  reindeer,  the  hare,  the  bear,  and  birds. 
Most  of  this  food  can  be  obtained  only  during  the  time  of  light,  which 
is  therefore  the  hunting  season.  Food  for  winter  is  preserved  easily 
because  of  the  cold.  Since  fuel  and  means  of  cooking  are  meager, 
much  meat  is  eaten  raw.  In  north  Greenland,  the  tiny  fire  —  a 
little  oil  with  a  wisp  of  grass  or  moss  for  a  wick  —  is  used  chiefly  for 
melting  snow  and  ice  for  drinking  water.  The  dependence  of  the 
people  on  animal  life  makes  them  hunters  and  fishers.  The  hunters 
are  partly  nomadic,  going  about  in  search  of  game  during  the  sum- 
mer, but  having  fixed  habitations  for  winter. 

Most  of  the  Eskimo 's  clothing  is  of  fur.  Plant  fibers  which  could 
be  woven  or  braided  together  are  unknown,  except  as  they  are  brought 
in  from  other  lands.  The  materials  used  in  making  dwellings  depend 
on  local  circumstances.  Where  forests  are  accessible,  as  along  the 
margin  of  the  zone,  or  where  driftwood  can  be  had  from  the  ocean, 
as  along  some  coasts,  wood  is  used.  Elsewhere,  the  winter  house  is 
usually  of  stone  or  snow.  During  the  hunting  season,  the  hunters 
live  in  tents  of  skins. 

Weapons  and  utensils  may  be  made  from  wood,  if  it  is  available; 
more  commonly  they  are  made  from  bone  and  hides.  The  use  of  these 
animal  products  is  the  characteristic  feature  of  the  arts  and  crafts  of 
the  Eskimos.  Perhaps  in  no  other  thing  is  their  skill  shown  better 
than  in  the  making  of  their  kayaks  (boats),  where  the  only  materials 
to  be  had  are  bone,  pieces  of  driftwood,  and  hides.  Out  of  these  they 
fashion  a  craft  wonderfully  adapted  to  the  uses  to  which  it  is  put. 

Looked  at  with  reference  to  their  surroundings,  the  Eskimos 
hardly  can  be  regarded  as  backward.  Probably  they  make  better 
use  of  the  things  at  their  command  than  more  highly  civilized  men 
could,  but  Arctic  climate  is  too  great  a  handicap  to  allow  them  to 
progress  far. 


QUESTIONS  139 

Questions 

1.  Why  is  rainfall  relatively  unimportant  in  affecting  the  distribution  of 
people  in  the  polar  regions? 

2.  If  the  entrance  from  the  Pacific  to  the  Arctic  Ocean  were  widened  greatly, 
what  would  be  the  probable  effect  on  the  climate  of  polar  North  America? 

3.  Suggest  reasons  why  the  Antarctic  has  been  less  well  explored  than  the 
Arctic  regions. 

4.  Why  do  trees  grow  in  higher  latitudes  in  Asia  than  in  North  America 
(Fig.  62)? 

5.  What  factors  determine  the  course  of  the  isotherm  of  50°  in  Fig.  62? 

6.  Why  is  there  an  ice-cap  over  central  Greenland  and  not  over  lands  in  the 
same  latitude  in  northern  Asia? 


CHAPTER  XII 
THE  OCEANS 

General  Considerations 

Importance  of  the  oceans.  The  oceans  are  of  great  importance 
to  the  rest  of  the  earth  in  many  ways.  Their  effects  on  temperature 
and  atmospheric  moisture  have  been  noted  (pp.  51,  57).  The  waves 
of  all  seas  are  constantly  wearing  away  the  land  in  some  places,  and 


Fig.  63.  Diagram  showing  destinations  of  exports  from  the  United  States 
by  continents  and  leading  countries  (1910).  (Values  in  millions  of  dollars;  per- 
centages are  proportions  of  total  exports.) 

building  new  land  elsewhere,  On  the  whole,  destruction  exceeds 
building,  so  far  as  land  is  concerned;  consequently,  the  ocean  tends 
to  increase  its  area  at  the  expense  of  the  land  (p.  348). 

The  oceans  are  an  important  source  of  food,  and  furnish  large 
amounts  of  other  useful  materials.     Thousands  of  people  are  em- 

140 


COMMERCE  OVER   THE   OCEAN  HIGHWAY        141 


ployed  in  getting  commercial  products  from  them.  Other  thousands 
are  engaged  in  the  carrying  trade  on  the  seas.  Formerly  the 
oceans  were  barriers  to  travel  and  communication,  but  swift  steam- 
ships and  cable  lines  now  make  communication  between  the  con- 
tinents easy.  The  voyage  across  the  Atlantic  formerly  took  as 
many  weeks  as  it  now  takes  days,  while  the  happenings  of  this 
morning  in  Europe  may  be  printed  in  the  evening  papers  of  Buenos 
Aires.  Nine-tenths  of  our  foreign  trade  is  carried  by  vessels. 
Enormous  quantities  of  goods  are  shipped  annually  to  the  United 
States  from  all  the  leading  countries  of  the  world,  and  from  the 
United  States  to  these  countries  (Figs.  63  and  64),  over  the  ocean 
highway. 

Distribution  and  area.     The  oceans  encircle  the  earth  in  latitude 
60°  S.  (Fig.  57),  and  the  waters  south  of  40°  S.  are  sometimes  called 


Fig.  64.  Diagram  showing  sources  of  imports  to  the  United  States  by  con- 
tinents and  leading  countries  (1910).  (Values  in  millions  of  dollars;  percentages 
are  proportions  of  total  imports.) 

the  Southern  Ocean.  From  it  the  Atlantic ,  Pacific,  and  Indian  oceans 
extend  northward  thousands  of  miles.  In  the  northern  hemisphere 
the  land  makes  an  almost  complete  circuit  in  latitude  60°  to  70°  (Fig. 
58),  whence  it  extends  southward  in  two  great  arms.  North  of 
latitude  about  70°  lies  the  Arctic  Ocean,  almost  surrounded  by  land 


142  THE    OCEANS 

(Fig.  62)  and  therefore  with  but  narrow  connections  with  the  larger 
oceans.     The  area  of  the  different  oceans  is  about  as  follows : 

Arctic  Ocean 5,200,000  square  miles 

Indian  Ocean 28,000,000  square  miles 

Atlantic  Ocean 35,000,000  square  miles 

Pacific  Ocean 67,000,000  square  miles 

Southern  Ocean 5,700,000  square  miles 

Exploration  of  the  ocean.  The  motions  of  the  surface  waters, 
such  as  waves  and  tides,  may  be  studied  from  the  shore,  but  it  has 
taken  the  work  of  many  exploring  expeditions  to  give  us  our  present 
knowledge  of  the  depths  of  the  ocean. 

The  depth  of  the  ocean  is  known  by  soundings,  which  are  made 
from  ships  by  reeling  out  a  heavy  weight  held  by  a  fine  steel  wire. 
A  sounding  of  3,000  fathoms  (a  fathom  =  6  feet)  can  be  made  in  about 
an  hour.  A  series  of  soundings  in  any  region  give  a  fairly  accurate 
idea  of  the  form  of  that  part  of  the  sea-floor. 

Small  samples  of  sediment  from  the  bottom  of  the  sea  are  brought 
to  the  surface  by  various  sorts  of  apparatus.  Larger  samples  of 
material  from  the  bottom  and  specimens  of  deep-sea  life  are  obtained 
by  dredges.  Another  device,  known  as  a  water-bottle,  is  used  to 
secure  samples  of  water  from  various  depths,  while  a  self-registering 
thermometer  records  the  temperatures  at  different  levels. 

Materials  of  the  bottom.  Most  of  the  sea-bottom  is  covered 
with  soft  sediment.  Some  of  it  was  carried  to  the  sea  by  rivers,  some 
was  worn  from  the  shores  by  waves,  some  was  blown  from  the  land, 
some  is  made  up  of  the  shells  and  skeletons  of  organisms  which  lived 
in  the  water,  and  some  consists  of  fine  debris  thrown  out  from  vol- 
canoes beneath  the  sea.  A  little  cosmic  ("shooting-star")  dust  is  also 
present.  Near  many  shores,  gravel  and  sand  from  the  land  cover  the 
bottom.  Beyond  the  gravel  and  sand,  fine  sediments,  such  as  mud 
and  clay,  prevail;  but  sediments  of  organic  origin  are  found  in  many 
places.  Thus  coral  reefs  and  mud  made  by  the  grinding  up  of  coral 
by  waves  are  found  in  shallow  water  in  many  places  in  low  latitudes. 

Ooze  is  the  name  applied  to  those  soft  materials  of  the  sea-bottom  composed 
largely  of  the  shells  and  other  hard  secretions  of  tiny  organisms  which  live  in  the 
water.  Many  of  them  live  near  the  surface,  and  their  shells  sink  when  the  organ- 
isms die.  The  various  oozes  are  named  from  the  animals  and  plants  which  con- 
tribute most  to  them. 

Below  the  depth  of  about  2,200  fathoms,  the  ocean-bottom  is 
covered  with  red  clay,  the  particles  of  which  came  from  many  sources. 


THE   DEPTHS   OF   THE   SEA  143 

Most  of  it  consists  of  the  decomposed  products  of  (i)  materials 
thrown  out  from  volcanoes,  (2)  dust  blown  from  the  land,  (3)  shells 
and  other  hard  parts  of  marine  life,  and  (4)  meteors. 

Depth  and  pressure.  The  average  depth  of  the  ocean  is  about 
two  and  one-half  miles,  or  nearly  13,000  feet.  The  depth  exceeds 
four  miles  in  many  places,  and  the  area  of  very  deep  water  is  much 
greater  than  that  of  very  high  land.  The  areas  which  are  far  below 
the  average  depth  of  the  ocean  are  known  as  deeps.  The  greatest 
depth  of  water  known,  32,078  feet,  is  in  the  Pacific  Ocean,  near  the 
Philippine  Islands.  This  depth  is  more  than  the  height  of  the  highest 
mountain  (Mt.  Everest,  29,002  feet)  above  the  sea.  There  are  other 
areas  exceeding  five  miles  in  depth  in  the  Pacific,  which  is  the  deepest 
ocean.  The  greatest  depth  of  water  known  in  the  Atlantic  is  Blake 
Deep  (27,366  feet),  north  of  Porto  Rico,  In  few  other  places  in  the. 
Atlantic  does  the  depth  reach  20,000  feet.  The  Indian  Ocean  is  not 
known  to  have  depths  much  exceeding  20,000  feet,  and  the  deepest 
known  places  in  the  Arctic  and  Antarctic  seas  are  still  less. 

The  pressure  at  the  bottom  of  the  oceans  is  very  great.  At  a 
depth  of  one  mile,  it  is  about  a  ton  to  the  square  inch,  while  in  the 
greatest  depths  it  is  six  tons.  This  pressure  would  crush  some  kinds 
of  stone.  Yet  the  ocean  water  does  not  become  much  denser  (is  not 
compressed  much)  even  under  so  great  pressure.  Objects  such  as 
pebbles,  which  sink  readily  at  the  surface,  sink  readily  to  the 
bottom. 

Topography  of  the  bottom.  The  surface  of  the  land  is  made 
rough  in  various  ways,  especially  by  running  water  andw^inds;  but 
most  of  the  sea-bottom  is  nearly  flat.  In  spite  of  its  general  flatness 
the  sea-bottom  has  many  irregularities,  for  there  are  (i)  volcanic  cones, 
some  of  them  built  up  from  the  bottom  of  the  deep  sea  to  elevations 
far  above  its  surface  (p.  194) ;  (2)  steep  slopes,  such  as  those  (a)  between 
the  continental  platforms  and  the  deep-sea  basins  and  (b)  about  some 
of  the  deeps;  (3)  valley-like  depressions,  especially  on  the  continental 
shelves;  (4)  great  ridges  somewhat  like  the  mountain  ridges  of  the  land; 
and  (5)  broad,  plateau-like  swells.  Submarine  slopes  as  great  as  i 
mile  in  8  are  rare,  and  i  mile  in  20  not  very  common.  The  latter 
would  make  a  steep  railway  grade. 

Volcanic  cones  are  most  numerous  in  the  Pacific  Ocean.  Many  of  the  valley- 
like depressions  on  the  continental  shelves  are  continuations  of  valleys  on  land. 
Thus  the  Hudson,  Delaware,  Susquehanna,  St.  Lawrence,  and  other  valleys  are 
continued  out  under  the  sea.     Such  submerged  valleys  are  thought  to  have  been 


144  THE   OCEANS 

formed  by  rivers  when  the  areas  where  they  occur  were  land.  Examples  of  moun- 
tain-like swells  are  furnished  by  Cuba  and  the  adjacent  islands,  which  are  really 
the  crests  of  a  great  mountain  system  rising  from  deep  water. 

Composition  of  sea-water.  One  hundred  pounds  of  average 
sea-water  contain  nearly  three  and  one-half  pounds  of  dissolved 
mineral  matter.  More  than  three-fourths  (nearly  78  per  cent)  of 
this  is  common  salt,  but  nearly  all  other  substances  found  in  the 
earth's  crust  are  present,  most  of  them  in  very  small  quantities. 
If  all  the  salts  dissolved  in  the  sea  were  taken  out  of  solution  and  laid 
down  as  solid  matter  on  the  ocean-bottom,  they  would  make  a  layer 
about  17s  feet  thick.  In  the  past,  the  evaporation  of  water  from 
salt  lakes,  perhaps  cut  off  from  the  sea  by  changes  of  level,  has  formed 
important  salt-beds.  New  York  has  a  valuable  salt  industry  near 
Syracuse,  depending  on  such  deposits  of  rock  salt  (p.  183). 

The  mineral  matter  in  sea-water  makes  it  a  little  heavier  than 
fresh  water,  and  makes  it  freeze  less  readily.  Its  lower  freezing  point 
(26°-28°  F.)  often  leaves  the  ocean  free  from  ice  when  nearby  bodies 
of  fresh  water  are  frozen  over. 

Sources  of  mineral  matter.  Dissolved  mineral  matter  is  being 
carried  to  the  sea  by  rivers  all  the  time,  and  they  have  brought  the 
sea  most  of  its  mineral  matter,  though  some  of  it  may  have  been  dis- 
solved from  rocks  beneath  the  sea,  or  about  its  shores.  The  mineral 
matter  carried  in  solution  to  the  sea  by  rivers  in  a  year  would  make 
nearly  half  a  cubic  mile  of  solid  matter.  Those  minerals  of  the  land 
which  are  dissolved  most  easily  get  into  rivers,  and  thence  to  the 
sea,  in  greater  quantity  than  those  which  are  less  soluble. 

Withdrawal  of  mineral  matter  from  the  sea.  Of  the  mineral 
matter  carried  in  solution  to  the  sea,  calcium  carbonate,  of  which 
most  shells  are  made,  is  most  important  to  ocean  life.  The  amount  of 
this  substance  dissolved  in  river-water  is  nearly  as  great  as  that  of 
all  others.  The  amount  of  common  salt  in  river-water  is  too  small 
to  be  tasted;  yet  the  amount  of  it  in  sea- water  is  more  than  200 
times  that  of  calcium  carbonate.  The  reason  is  that  calcium  carbon- 
ate is  taken  out  of  the  water  all  the  time  by  animals,  to  make  shells, 
coral,  etc.,  while  most  of  the  salt  carried  to  the  sea  stays  in  the  water; 
and  this  probably  has  been  true  for  millions  of  years. 

Gases  in  sea-water.  Sea-water  also  contains  dissolved  gases, 
the  most  abundant  being  nitrogen,  oxygen,  and  carbon  dioxide.  The 
amount  of  oxygen  dissolved  in  the  ocean  is  more  than  1/300  of  that 
in  the  air;  the  amount  of  nitrogen  about   i/ioo  that  of  the  air. 


TEMPERATURE   OF   THE   SEA  145 

while  the  amount  of  carbon  dioxide  in  the  sea  is  18  times  that  in 
the  air.  Much  of  the  gas  in  the  ocean  was  dissolved  from  the 
atmosphere. 

The  oxygen  of  the  water  is  being  used  all  the  time  by  sea  animals, 
and  its  supply  is  being  renewed  all  the  time  by  solution  from  the  air. 
Animals  and  plants  do  not  use  the  nitrogen  dissolved  in  sea-water, 
and  the  same  nitrogen  probably  stays  there  from  age  to  age.  The 
carbon  dioxide  is  being  used  all  the  time  by  the  plants  of  the  sea,  and 
some  of  it  is  constantly  escaping  into  the  air. 

Salinity,  density,  and  movement.  For  several  reasons,  some 
parts  of  the  sea  are  more  salty  than  others,  (i)  The  salt  is  left  behind 
when  ocean-water  evaporates.  Since  evaporation  is  more  rapid  in 
some  places  than  in  others,  the  water  becomes  more  salty  where 
evaporation  is  great,  as  in  some  hot  climates.  (2)  Where  much  rain 
falls,  and  (3)  where  large  rivers  enter,  the  sea-water  is  freshened. 
In  these  ways  the  saltness  of  the  sea-water  at  the  top  of  the  ocean  is 
changed  all  the  time. 

Every  change  in  the  saltness  of  sea- water  changes  its  density,  and 
unequal  density  causes  movement.  When  surface  water  becomes 
denser  than  that  beneath,  it  sinks,  and  lighter  water  comes  in  over 
it  from  all  sides.  When  the  surface  water  of  one  place  becomes  less 
dense  (fresher)  than  that  about  it,  the  lighter  water  spreads  out  on 
the  surface,  as  oil  spreads  on  water.  Since  variations  in  saltness  are 
being  produced  all  the  time,  motion  due  to  unequal  density  is  constant. 
Movements  brought  about  in  this  way  are  usually  very  slow. 

Temperature  of  the  Sea 

Temperature  of  the  surface.  The  surface  of  the  ocean,  like 
that  of  the  land,  is  warmer  near  the  equator  and  cooler  toward  the 
poles  (Fig.  65).  Near  the  equator  its  temperature  is  about  80°  F.; 
near  the  poles,  where  not  frozen,  it  is  26°-28°  F.  When  frozen,  the 
surface  of  the  ice  may  become  as  cold  as  the  air  above  it ;  but  the  tem- 
perature of  the  water  just  beneath  the  ice  is  26°-28°  F.  The  de- 
crease of  temperature  toward  the  poles  is  by  no  means  regular,  as 
shown  by  the  isothermal  chart  (Fig.  65). 

In  the  open  sea,  ocean  currents  help  to  make  the  isotherms 
depart  from  the  parallels  (p.  51).  Some  currents  are  cold,  flow- 
ing into  warmer  water,  and  some  are  warm,  flowing  into  cooler 
water. 


146 


THE  OCEANS 


Rivers  help  to  make  surface  temperatures  unequal,  for  many  of 
them  are  warmer  than  the  sea  in  summer,  and  colder  in  winter.  Part- 
ly enclosed  arms  of  the  sea  in  low  latitudes  are  warmer  than  the  open 
ocean  in  the  same  latitude. 

Temperature  and  movement.  Water  expands  slightly  when 
warmed.  Warm  water  is  therefore  lighter  than  cold  water,  if  both 
are  equally  salt.  It  follows  that  unequal  surface  temperatures  cause 
movement  of  the  surface  waters,  and  since  the  surface  temperature 
is  kept  unequal  all  the  time  by  unequal  heating,  by  inflow  of  rivers, 


Fig.  65.     Map  showing  mean  annual  temperatures  for  the  surface  waters  of 
the  oceans.     (After  Lyde.) 


and  by  melting  ice,  there  is  constant  though  slow  movement  of  the 
surface  waters. 

Temperature  beneath  the  surface.  Sea-water  becomes  cooler 
with  increasing  depth,  except  where  the  surface  is  at  or  near  the 
freezing  point.  Even  where  the  surface  w^ater  is  warmest,  the 
temperature  at  a  depth  of  a  few  hundred  fathoms  is  below  40°  F. 

It  is  estimated  that  not  more  than  one-fifth  of  the  water  of  the 
ocean  has  a  temperature  as  high  as  40°  F.,  while  its  average  tempera- 
ture is  probably  below  39°  F.  Only  in  certain  areas  of  shallow  water, 
and  in  the  partly  enclosed  seas  of  relatively  low  latitudes,  is  the  tem- 
perature of  the  water  at  the  bottom  as  high  as  40°. 


WAVES,  CURRENTS,  AND   TIDES  .147 

Movements  of  Sea- Water 
Causes 

We  have  seen  that  differences  in  saltness  and  in  temperature 
make  waters  unequal  in  density,  and  so  produce  a  slow  circulation  of 
the  waters  of  the  sea.  There  are  other  things  which  produce  move- 
ment, such  as  (i)  differences  of  level,  (2)  winds,  (3)  the  attraction  of 
the  moon  and  the  sun,  and  (4)  occasional  causes,  like  earthquakes 
and  volcanic  explosions. 

Inequalities  of  level.  The  inequalities  of  level  wnicn  produce 
movements  of  sea- water  are  brought  about  chiefly  by  (i)  the  in- 
flow of  rivers,  which  raises  the  surface  of  the  sea  near  their  mouths; 
(2)  winds,  which  pile  up  the  water  along  the  shores  against  which 
they  blow;  (3)  unequal  rainfall,  which  raises  the  surface  most  where 
most  rain  falls;  and  (4)  unequal  evaporation,  which  lowers  the  sur- 
face most  where  it  is  greatest. 

Movements  due  to  unequal  rainfall  and  evaporation  are  too  slight 
to  be  seen.  Those  caused  by  the  inflow  of  rivers  and  by  winds  are 
greater.  Thus,  beyond  the  mouth  of  a  great  river  like  the  Amazon, 
movement  may  be  distinct  for  many  miles,  and  waters  often  are  piled 
up  against  a  shore  by  winds,  so  that  the  rise  is  seen  readily.  The 
raising  of  the  surface  of  the  water  caused  most  of  the  destruction  in 
the  storm  at  Galveston  (p.  92).  When  the  water-level  along  a  coast 
has  been  raised  by  the  wind,  it  settles  back  after  the  wind  goes  down. 
Since  the  causes  producing  differences  of  level  are  always  in  operation, 
movements  due  to  these  differences  are  always  taking  place. 

Winds.  Winds  produce  movement  of  sea-water  in  another  way. 
Where  they  have  a  constant  direction,  as  in  the  zone  of  trades  (p.  105), 
there  is  a  constant  drifting  movement  of  surface  water  in  one  direc- 
tion. A  steady  movement  in  one  direction  necessitates  a  return  move- 
ment somewhere  else,  thus  producing  a  circulation  of  the  sea-water. 
Where  the  circulation  is  in  the  form  of  distinct  streams  of  water,  they 
are  called  ocean  currents. 

Attraction  of  moon  and  sun.  Bodies  attract  each  other  in 
proportion  to  their  masses,  and  inversely  as  the  squares  of  their 
distances.  That  is,  a  body  which  weighs  twice  as  much  as  another 
has  twice  the  attractive  force  at  the  same  distance.  If  one  of  two 
bodies  of  the  same  mass  (or  weight)  is  twice  as  far  from  a  third  body 
as  the  other  is,  their  attractive  forces  on  the  third  are  as  1:4. 

The  side  of  the  earth  toward  the  moon  is  nearer  the  moon  (  by 


148  THE  OCEANS 

about  4,000  miles)  than  the  center  of  the  earth  is,  and  so  is  attracted 
by  that  body  more  strongly  than  the  center.  The  opposite  side  (about 
4,000  miles  farther  away)  is  attracted  less  strongly  than  the  center, 
and  these  differences  of  attraction  disturb  the  waters  of  the  earth. 
The  attraction  of  the  sun  produces  similar,  though  lesser,  effects. 
Movements  of  the  sea-water,  known  as  Odes,  are  the  result. 

Occasional  causes.  Landslides  along  shore,  earthquakes,  and 
volcanic  explosions  may  cause  sudden  and  extensive  movements  of 
the  ocean-water  (pp.  191,  197).  Low  coastal  lands  occasionally 
suffer  severely  from  movements  of  this  sort. 

Types  of  Movement 

The  principal  movements  which  result  from  the  above  causes  are 
(i)  waves,  with  the  undertow  and  shore  currents  (p.  346)  which  they 
produce;  (2)  ocean  currents;  (3)  drift,  or  feeble  currents;  and  (4)  tides. 

Waves.  When  the  wind  blows  over  a  water  surface  it  causes 
waves.  The  stronger  the  winds,  the  greater  the  waves.  With 
moderate  winds,  waves  in  open  water  rarely  exceed  10  feet  in  height 
(from  crest  to  trough).  Ordinary  storm- waves  may  be  twice  as  high, 
while  in  violent  storms  a  height  of  40  or  more  feet  is  attained.  Such 
waves  breaking  on  the  decks  of  vessels  may  do  much  damage.  Storm- 
waves  travel  30  to  60  miles  an  hour,  but,  save  in  shallow  water,  the 
water  in  a  wave  usually  does  not  move  forward  (p.  346). 

The  distance  between  successive  wave  crests  is  the  length  of  the 
wave.  Wave  lengths  vary  from  100  feet  or  less,  to  2,000  feet  or  more 
in  severe  storms.  Occasionally  the  surface  of  the  ocean  is  smooth  and 
glassy,  and  yet  shows  long,  low  undulations.  These  are  "swells," 
and  usually  represent  waves  caused  by  distant  storms.  On  some 
coasts  they  interfere  seriously  with  commerce.  Short,  "choppy" 
waves  are  especially  unfavorable  for  small  craft,  and  may  cause  much 
discomfort  to  passengers  on  larger  vessels.  In  general,  the  longer  the 
vessel,  the  less  it  is  affected  by  waves;  hence  the  advantage  of  the 
modern  ocean  steamships,  which  in  many  cases  are  twice  as  long 
(700  to  800  feet)  as  the  average  storm-wave. 

Currents  and  drifts.  There  are  more  or  less  distinct  streams 
of  water,  or  currents,  in  various  parts  of  the  ocean.  This  was  known 
first  by  their  effect  on  the  course  of  sailing  vessels.  It  was  later  proved 
in  other  ways,  as  by  following  the  course  of  floating  objects  set  adrift 
for  this  purpose. 

The  course  of  currents  is  important  because  of  their  effect  on  navi- 


THE    GULF   STREAM  149 

gation.  I-n  foggy  weather,  and  especially  near  some  coasts,  failure  to 
allow  for  the  current  may  lead  to  ship-wreck.  Some  of  the  wrecks 
that  have  occurred  on  the  Irish  coast  probably  were  caused  in  this 
way.  Vessels  are  aided  or  retarded  by  currents,  according  to  the 
direction  of  the  voyage.  Surface  currents  affect  the  movements  of 
icebergs  and  floe-ice.  Collision  with  an  iceberg  may  wreck  the 
largest  steamship,  as  the  Titanic,  and  floating  ice  favors  the  forma- 
tion of  fog,  which  increases  the  danger  of  collision.  For  these  reasons, 
steamship  routes  across  the  North  Atlantic  vary  somewhat  with  the 
season,  in  order  to  avoid  the  floating  ice. 

Little  is  known  of  ocean  currents  beneath  the  surface.  Most  of 
them  are  shallow,  compared  with  the  depth  of  the  ocean.  A  current 
so  slow  as  to  be  indistinct  often  is  called  drift. 

Courses  and  causes  of  ocean  currents.  Fig.  66  shows  the 
general  circulation  of  the  surface  waters  of  the  sea.  It  represents  a 
large  part  of  the  surface  water  as  moving.  There  are  equatorial 
currents  or  drifts  moving  westward,  one  on  each  side  of  the  equator, 
in  both  the  Atlantic  and  Pacific  oceans.  The  westward-drifting  equa- 
torial waters  of  the  Atlantic  are  divided  at  the  coast  of  South  America. 
The  smaller  part  is  turned  to  the  southwest,  and  the  larger  part  to  the 
northwest,  along  the  border  of  the  continent.  Part  of  the  northern 
branch  flows  through  the  Caribbean  Sea  into  the  Gulf  of  Mexico, 
whence  it  issues  through  the  narrow  strait  between  Cuba  and  Florida 
as  the  Gulf  Stream.  This  well-defined  current  is  fed  partly  by  the 
water  which  enters  the  Gulf  from  the  equatorial  drift,  and  partly  by 
that  which  enters  from  the  land. 

In  the  Straits  of  Florida,  the  Gulf  Stream  is  about  40  miles  wide  in  its  nar- 
rowest part,  2,000  to  3,000  feet  deep,  and  has  a  maximum  velocity  of  about  five 
miles  per  hour.  Farther  north  it  becomes  wider  and  slower,  until,  in  the  open 
ocean,  the  rate  is  perhaps  only  10  to  15  miles  per  day.  As  it  becomes  slow,  its 
boundaries  become  less  distinct,  and  it  is  recognized  by  its  temperature,  color; 
and  life  more  readily  than  by  its  motion. 

As  it  advances,  the  Gulf  Stream  turns  toward  the  east  (to  the 
right),  crosses  the  Atlantic,  and  approaches  the  coast  of  Europe  in  a 
latitude  farther  north  than  that  where  it  leaves  the  coast  of  America, 
As  it  approaches  Europe,  it  divides  and  spreads,  but  long  before 
Europe  is  reached  (about  latitude  40°  N.),  the  current  has  become 
a  widespread  drift  of  water,  not  easily  distinguished.  This  favorable 
current  and  the  westerly  winds  make  the  voyage  for  sailing  vessels 
from  this  country  to  England  much  quicker  than  the  return  trip. 


I50  THE  OCEANS 

That  part  of  the  equatorial  drift  which  is  turned  southward  along  the 
coast  of  South  America  soon  turns  to  the  left  (Fig,  66). 

The  equatorial  drifts  of  the  Pacific  follow  courses  similar  to  those 
of  the  Atlantic.  The  part  which  turns  north  is  the  Japan  Current. 
The  Indian  Ocean  has  a  south  equatorial  drift  only,  and  its  course 
corresponds  to  that  of  the  southern  part  of  the  equatorial  drifts  of 
the  other  oceans.  All  currents  moving  toward  the  poles  from  the 
equatorial  region  are  warm  currents. 

The  movement  of  warm  waters  into  the  polar  oceans  makes  a  return 
movement  necessary.  Cold  waters  moving  equatorward  from  these 
oceans  are  turned  to  the  right  in  the  northern  hemisphere,  and  to 
the  left  in  the  southern.  The  result  is  to  throw  them  to  the  eastern 
coasts  of  the  continents,  where  in  places  they  form  distinct  cold 
currents.  Along  the  east  coast  of  North  America,  the  Labrador  Cur- 
rent sometimes  brings  icebergs  south  to  latitude  40°,  while  in  the  warmer 
waters  of  the  northeastern  Atlantic,  drift-ice  rarely  is  encountered 
south  of  latitude  70°.  The  Labrador  Current  chills  the  air  above  it, 
and  this  helps  to  make  northeast  winds  in  New  England  cold. 

The  equatorial  drifts  are  caused  and  directed  by  the  trade-winds. 
Outside  the  tropics  the  winds  do  not  blow  in  one  direction  all  the 
time,  and  so  do  not  produce  persistent  drifts  or  currents.  In  regions 
of  strong  monsoon  winds,  as  about  India,  the  drift  of  the  surface 
waters  changes  with  the  wind. 

If  the  ocean  covered  all  the  earth,  the  westward  drift  of  equatorial 
waters  caused  by  the  trade-wnnds  would  go  round  and  round  the 
earth.  But  the  continents  deflect  the  waters,  turning  them  north 
and  south.  Once  turned  in  these  directions,  the  waters  would  tend 
to  follow  the  coasts  but  for  the  deflecting  influence  of  the  earth's 
rotation.  Where  the  sea  is  so  shallow  that  the  moving  water  touches 
bottom,  the  topography  of  the  bottom  influences  the  course  of  move- 
ment. Ocean  currents  therefore  appear  to  be  started  chiefly  by  the 
winds,  and  to  be  directed  by  winds,  lands,  and  the  rotation  of  the 
earth,  and,  to  a  less  extent,  by  the  topography  of  the  bottom. 

Ocean  currents  and  atmospheric  temperatures.  Without  ocean 
currents,  the  isotherms  over  the  sea  would  follow  the  parallels  some- 
what closely,  except  near  the  continents  (p.  51).  Under  such 
conditions,  the  temperature  over  the  ocean  in  the  latitude  of 
the  British  Isles  and  northward  would  be  10°  F.  or  more  lower 
than  now  (Fig.  65).  Ocean  currents  do  not  themselves  warm  or 
cool  the  land;  but  the  air  over  a  warm  current  is  warmed  by 


THE  CURRENTS   OF  THE  SEA 


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152  THE  OCEANS 

the  water,  and  is  then  blown  to  the  land.  Even  without  the 
Gulf  Stream,  the  western  coast  of  Europe  would  have  a  milder  winter 
climate  than  the  eastern  coast  of  North  America  in  the  same  latitudes 
(p.  51),  but  the  drift  of  warm  water  into  the  North  Atlantic  makes 
the  winter  temperature  of  Europe  north  of  latitude  50°  considerably 
warmer  than  it  would  be  otherwise.  Thus  the  harbor  of  Hammer- 
fest,  Norway,  Lat.  76°,  is  affected  by  ice  little  more  than  that  of 
New  York,  Lat.  40°.  The  Japan  Current  likewise  lessens  the  cold 
of  winter  on  the  northwestern  coast  of  North  America. 

Warm  currents  often  help  to  cause  fogs,  both  at  sea  and  on  land. 
When  wind  blows  over  a  warm  current,  it  takes  up  a  large  supply 
of  moisture.  If  it  then  blows  over  colder  water,  it  is  cooled,  and  some 
of  its  moisture  is  condensed,  producing  a  fog.  Fogs  are  common 
along  the  Gulf  Stream,  especially  where  the  adjacent  land  or 
water  is  much  cooler  than  the  current  itself.  Fogs  are  more  abun- 
dant about  Newfoundland  than  farther  south,  because  the  difference 
between  the  temperature  of  the  Gulf  Stream  and  its  surroundings  is 
greater  there  than  farther  south. 

Tides.  Along  most  coasts  the  ocean-water  rises  and  falls  twice 
every  day,  or,  more  exactly,  every  24  hours  and  52  minutes.  The  rise 
and  fall  of  the  water  are  the  tides.  The  tide  rises  for  about  six  hours, 
when  it  is  high  or  flood  tide,  and  then  falls  for  about  six  hours,  when  it 
is  low  or  ebb  tide.  In  most  places  there  is  a  distinct  interval  of  little 
or  no  movement  ("slack  water")  when  high  tide  changes  toward  low, 
and  vice  versa.  The  rise  and  fall  amount  to  several  (3  to  6)  feet  in 
most  places.  In  bays  which  open  broadly  to  the  sea,  but  are  narrow 
at  their  heads,  the  range  is  sometimes  20  or  30  feet,  and  in  rare  cases, 
as  in  the  Bay  of  Fundy  (Figs.  67  and  68),  50  feet  or  more.  Where  bays 
have  a  narrow  entrance  and  widen  within,  the  tidal  range  is  small. 
Tides  are  absent  in  small  lakes,  and  are  feeble  in  large  lakes  and  in 
seas  connected  with  the  ocean  by  a  narrow  passage,  such  as  the 
Mediterranean  Sea  and  the  Gulf  of  Mexico. 

In  many  shallow  harbors  the  tides  have  an  important  effect  on 
navigation  (Figs.  67  and  68).  Even  some  of  the  most  important 
ports  depend  on  the  rise  of  the  tide  for  the  movement  of  their  com- 
merce. Thus  at  Liverpool  vessels  arriving  at  low  tide  must  wait,  in 
jffiany  cases,  for  high  tide,  before  the  water  is  deep  enough  for  them  to 
dock,  and  vessels  must  arrange  hours  of  departure  to  match  high  tides. 
Where  the  tide  runs  in  among  islands,  or  passes  through  narro\r 
straits,  it  causes  distinct  currents  {tidal  races),  eddies,  and  whirlpools. 


TIDES  AND   COMMERCE 


153 


like  the  famous  Maelstrom  near  the  Lofoten  Islands.  Sailing  vessels 
frequently  have  serious  difficulties  with  tidal  races,  as  at  Hell  Gate, 
New  York,  and  in  Vineyard  and  Nantucket  sounds,  off  the  coast  of 


i^ZJj^^ 

Fig.  67.  Low  tide  at  Wolfeville,  Bay  of  Fundy,  Nova  Scotia,  Sept.,  iQO.v 
In  March,  1904,  the  end  of  the  pier  was  washed  away  in  a  storm,  and  the  light- 
house was  damaged.     (Roland  Hayward.) 


Massachusetts.     Fishermen  commonly  speak  of  the  tide  as  "coming 

going  out,"  and  time  their  movements  to  take  advantage  of 

In  many  ways  tides  are  more  important  to  navigation  than  ocean 


in,"  or  " 


It 


Fig.  68.    High  tide  at  the  same  place  shown  in  Fig.  67.     (Roland  Hayward.) 

currents,  and  much  effort  is  devoted  to  charting  them  for  the  benefit 
of  navigators. 

The  tide  runs  far  up  many  rivers.  At  Troy,  some  150  miles  up 
the  Hudson  River,  the  range  of  the  tide  is  more  than  two  feet,  and 
tides  ascend  the  St.  Lawrence  nearly  300  miles. 


154  THE   OCEANS 

It  is  at  least  two  thousand  years  since  the  moon  was  first  thought  to  cause  the 
tides,  but  only  about  two  hundred  years  since  Newton  explained  how  the  moon 
produces  them.  Without  attempting  to  give  a  full  explanation  of  the  tides,  some 
of  the  principles  involved  may  be  understood.  If  a  weight  is  attached  to  a  string 
and  whirled,  it  tends  to  fly  away  in  a  straight  line.  It  is  prevented  from  doing  so 
by  the  string,  which  holds  it  in  its  circular  path.     The  tendency  to  fly  away  is  what 


0 


Fig.  69.  Diagram  to  show  the  tendency  of  the  moon  to  raise  the  water  on 
the  side  of  the  earth  toward  the  moon  and  on  the  opposite  side  at  the  same  time, 
producing  two  high  tides. 

is  called  centrifugal  force.  The  earth  and  moon  attract  each  other  (p.  147),  and 
would  fall  together  but  for  the  centrifugal  force  due  to  their  motions.  At  the 
center  of  the  earth,  and  at  the  center  of  the  moon,  the  attraction  between  these 
bodies  is  exactly  balanced  by  the  centrifugal  force  due  to  their  revolutions.  The 
result  is  that  neither  falls  toward  the  other.  But  on  the  side  of  the  earth  nearest 
the  moon  the  attraction  is  stronger  than  at  the  center  of  the  earth  (p.  148),  and  is 
greater  than  the  centrifugal  tendency.  The  attraction  of  the  moon,  therefore,  tends 
to  make  the  earth  bulge  out  on  the  side  nearest  the  moon.  On  the  opposite  side  of  the 
earth  the  attraction  is  weaker  than  at  the  center,  and  is  less  than  the  centrifugal 
force.  Here,  too,  the  earth  tends  to  bulge  out.  The  solid  part  of  the  earth  is  so 
rigid  that  it  does  not  rise  enough  to  be  felt  or  seen.     But  the  waters  of  the  ocean 


M^^ A         E     \\B 


Fig.  70.  Diagram  to  show  the  relative  positions  of  the  earth,  moon,  and  sun, 
at  the  time  of  new  moon  (  =  spring  tide).  Size  of  moon  (M)  and  earth  (E)  great- 
ly exaggerated. 

move  easily,  and  rise  a  little,  and  the  rise  takes  place  on  opposite  sides  of  the 
earth  at  the  same  time.  This  makes  the  high  tides.  Between  the  high  tides  the 
water  sinks  a  little,  making  the  low  tides.  The  rotation  of  the  earth  makes  the  tides 
appear  to  move  about  the  earth. 

If  all  the  earth  were  covered  with  water,  its  surface  would  have  two  great  tidal 
bulges  or  waves  at  the  same  time  (Fig.  69).  The  highest  part  of  one  would  be  a 
point  directly  under  the  moon,  and  the  highest  point  of  the  other  would  be  opposite 
the  first.  Each  wave  would  cover  half  the  earth,  and  the  borders  of  the  two  would 
meet  in  a  great  circle,  where  the  surface  of  the  water  would  be  lowest. 

If  the  moon  were  not  revolving  about  the  earth,  high  tide  at  any  place  would 
come  every  12  hours.     But  the  moon  moves  forward  in  its  orbit  about  the  earth. 


THE   CAUSE   OF  THE  TIDES  155 

so  that  it  takes  24  hours  and  52  minutes  for  a  given  place  to  have  the  same  relation 
to  the  moon  that  it  had  the  day  before.  This  makes  the  period  between  successive 
high  tides  1 2  hours  and  26  minutes. 

The  movements  of  the  tides  are  not  so  simple  as  the  outline  above  would  imply. 
Many  things  interfere.  The  continents  stop  or  divert  the  advance  of  tidal  waves, 
and  the  waves  travel  more  slowly  in  shallow  than  in  deep  water  (Why?).  Since 
tides  are  retarded  most  near  land,  their  advance  is  here  most  irregular.  For  these 
reasons,  the  time  of  high  tide  at  most  places  differs  from  the  time  when  the  moon 


Fig.  71.     Diagram  to  show  the  relative  positions  of  the  earth,  moon,  and  sun, 
at  the  time  of  full  moon  (=  spring  tide). 

crosses  their  respective  meridians.  This  difference  in  the  time  of  arrival  of  high 
or  low  tide  may  be  determined  for  any  harbor,  and  is  called  the  "establishment  of 
the  port."  At  New  York,  for  example,  high  water  arrives  8  hours  and  13  minutes 
after  the  moon  passes  the  meridian.  Tables  showing  the  "establishment"  of 
different  ports  are  of  great  value  to  navigators. 

The  sun  also  attracts  the  earth,  and  tends  to  cause  tides.     If  there  were  no  moon 
there  would  still  be  small  tides  produced  by  the  sun.     The  tides  which  we  know 


Fig.  72.  Diagram  showing  the  tendency  of  the  sun  and  moon  to  produce 
tides  on  opposite  parts  of  the  earth  at  the  time  half  way  between  new  moon  and 
full  moon,  and  half  way  between  full  moon  and  new  moon. 

are  the  combined  effects  of  moon  and  sun,  but  the  moon's  tides  are  much  the 
stronger.  The  sun  strengthens  the  tides  when  sun  and  moon  work  together,  and 
weakens  them  when  they  work  against  each  other. 

When  sun  and  moon  stand  in  the  relation  to  each  other  and  to  the  earth  shown 
in  Fig.  70  {new  moon),  each  tends  to  make  high  tides  at  A  and  at  B.  When  the 
relations  are  those  shown  in  Fig.  71  {full  moon),  the  result  is  the  same.  At  these 
times,  and  each  occurs  once  a  month,  high  tides  are  higher,  and  low  tides  lower, 
than  at  other  times.  The  tides  of  such  times  are  called  spring  tides.  They  have 
no  relation  to  the  spring  season. 

When  the  earth,  moon,  and  sun  have  the  relative  positions  shown  in  Fig.  72, 
end  this  occurs  twice  each  month,  the  tidal  influences  of  the  sun  and  the  moon  are 


156  THE  OCEANS 

opposed  to  each  other,  and  the  result  is  that  high  tides  are  not  so  high,  nor  low 
tides  so  low,  as  under  other  conditions.  The  tides  of  such  times  are  known  as 
neap  tides.     Spring  tides  have  nearly  twice  the  range  of  neap  tides  in  many  places. 

In  the  open  ocean  and  along  precipitous  coasts,  the  tide  is  like 
other  waves,  merely  a  rising  and  falling  of  the  water.  Like  other 
waves  also,  the  water  of  the  tidal  wave  moves  forward  when  it  ap- 
proaches shores  where  the  water  is  shallow. 

In  shallow  waters  near  the  coast,  tides  alternately  cover  and 
expose  wide  expanses  of  sandy  beach  or  mud  flats,  as  the  case  may 
be.  The  water-line  at  low  tide  may  be  a  quarter  of  a  mile  or  more 
from  its  position  at  high  tide.  Tidal  currents  may  be  effective  agents 
of  erosion,  maintaining  deep  channels  in  harbors,  to  the  great  ad- 
vantage of  commerce.  By  the  circulation  they  cause,  tides  in 
some  cases  help  to  remove  filth  which  otherwise  would  accumulate  in 
harbors.  Sewage  disposal  is  always  easier  for  cities  near  tide-water. 
On  the  other  hand,  the  sediment  drifted  about  by  tides  may  be  de- 
posited in  harbors.  This  makes  expensive  dredging  necessary,  in 
order  to  maintain  a  sufiicient  depth  of  water  for  shipping.  The 
frequent  shifting  of  the  deposits  renders  it  impossible  to  indicate  the 
channel  on  the  pilot  charts  of  some  harbors. 

The  large  volume  of  water  rising  and  falling  in  tides  has  led  to 
many  attempts  'o  develop  tidal  water  power.  Small  tide-mills  are 
used  for  grinding  grain  and  other  purposes  at  various  places  in  western 
Europe,  and  a  few  larger  power  plants  have  proved  useful,  as  in  the 
Seine  estuary. 

The  Life  of  the  Sea 

Animals  and  plants  abound  at  and  near  the  surface  of  the  sea, 
and  at  the  bottom  where  the  water  is  shallow.  A  bucket  of  water 
dipped  up  from  the  surface  of  the  ocean  almost  anywhere  will  con- 
tain hundreds  or  even  thousands  of  minute  plants  and  animals,  though 
most  of  them  are  too  small  to  be  seen  without  a  microscope.  Liv- 
ing things  are  present,  but  not  in  great  numbers,  at  the  bottom  of 
the  deep  sea;  but  in  the  water  between  the  uppermost  loo  fathoms 
and  the  bottom,  there  is  little  life. 

The  temperature,  the  depth,  the  clearness,  the  saltness,  and  the 
quietness  or  roughness  of  the  water,  influence  the  life  which  it  con- 
tains, in  ways  easily  understood.  The  depth  of  the  water  has  little 
or  no  effect  on  plants  and  animals  which  float  or  swim  near  the  sur- 
face; but  at  great  depths  the  supply  of  oxygen  is  slight,  and  there 


THE  LIFE  OF  THE  SEA  157 

is  not  light  enough  so  that  animals  can  see  much  below  50  fathoms. 
In  the  great  body  of  the  ocean  darkness  reigns,  and  green  plants, 
which  depend  directly  on  sunlight,  cannot  live  in  darkness. 

Though  the  pressure  of  the  water  at  the  bottom  of  the  ocean  is 
very  great  (p.  143),  the  animals  living  there  can  stand  it  because  their 
bodies  are  full  of  liquids  under  the  same  pressure,  and  these  great 
pressures  within  their  bodies  balance  the  great  pressures  without. 
If  an  animal  from  the  bottom  of  the  deep  sea  were  brought  suddenly 
to  the  surface  it  would  explode  (Why?).  Even  when  raised  slowly, 
they  sometimes  explode  as  they  near  the  surface. 

Some  animals,  such  as  the  polyps  which  make  coral,  live  only  in 
warm  regions.  Others,  such  as  narwhals  and  seals,  are  found  only 
in  cold  waters.  Still  others  are  found  in  both  warm  and  cold  waters. 
The  unequal  distribution  of  ocean  temperatures  by  warm  and  cold 
currents  influences  greatly  the  character  of  marine  life  in  different 
parts  of  the  sea. 

In  many  ways  the  life  of  the  sea  is  in  strong  contrast  with  that  of 
the  land.  Thus  most  familiar  land  plants  are  fixed  in  position,  but 
many  sea  plants  float.  Most  land  animals  are  free  to  move  about, 
while  many  of  those  in  the  sea,  such  as  polyps  and  barnacles,  are 
fixed  through  most  of  their  lives.  Many  which  are  not  fixed  move 
about  but  little,  either  lying  on  the  bottom  or  burrowing  into  it. 
Some,  on  the  other  hand,  as  many  of  those  in  the  surface  waters, 
appear  to  be  moving  always. 

All  the  great  groups  of  animal  life  are  represented  in  the  sea. 
Even  warm-blooded  mammals  (whales,  seals,  walruses,  etc.)  abound 
in  frigid  waters,  among  icebergs  and  ice-floes.  Some  of  them,  like 
the  seals  and  walruses,  do  not  spend  all  their  time  in  the  water,  but 
frequently  crawl  up  on  the  ice  or  land. 

Not  only  are  there  many  varieties  of  marine  plants  and  animals, 
but  the  largest  modern  animals  (whales)  live  in  the  sea.  Many  sea 
plants,  too,  are  of  great  size.  Some  sea-weeds  are  six  inches  in  diam- 
eter, and  some  have  a  length  greater  than  that  of  the  tallest  trees. 

The  total  value  of  food  products — -fish,  oysters,  clams,  crabs,  lob- 
sters, etc. — derived  from  the  sea  probably  is  not  less  than  $500,000,- 
000  per  year.  The  best  fishing  regions  are  found  where  large  areas  of 
shallow  water,  as  over  broad  continental  shelves,  furnish  extensive 
feeding  and  breeding  grounds  for  vast  numbers  of  fish.  The  most 
important  region  of  this  sort  is  the  area  of  shallow  water  about  the 
British  Isles,  including  the  North  Sea.     The  British  fisheries  employ 


158 


THE  OCEANS 


more  than  100,000  men,  and  yield  an  annual  catch  valued  at  more 
than  $50,000,000.  Similar  conditions  led  to  the  development  of  im- 
portant fisheries  from  New  England  (p.  375). 

Other  sea  animals  furnish  other  articles  of  commerce.  The  seal 
furnishes  fur  and  oil;  the  whale,  oil  and  whalebone;  and  the  hide  of 
the  walrus  makes  exceptionally  strong  leather.  Coral  and  sponges, 
products  of  animal  life,  are  also  articles  of  commerce.     Sea-weed  was 


Fig.  73.     Coral  formations,  Samoa.     (Muir  and  Moodie.) 


used  formerly  as  the  chief  source  of  soda  and  of  iodine.  Some  varieties 
still  are  gathered  in  large  quantities  on  the  coast  of  Massachusetts 
and  Europe,  to  be  used  as  food  under  the  name  of  "Irish  moss." 

Coral  reefs.  The  little  polyps  (Fig.  73)  which  secrete  coral 
live  where  the  water  (i)  is  120  feet  or  less  in  depth,  (2)  is  never  colder 
than  about  68°  F.,  (3)  has  the  saltness  of  normal  sea- water,  (4)  is 
free  or  nearly  free  from  sediment,  and  (5)  is  subject  to  some  movement 
by  the  wind.  Where  these  conditions  exist,  polyps  thrive  and  make 
reefs,  and  the  reefs  may  become  islands.  Polj'ps  flourish  along  the 
borders  of  many  tropical  lands,  and  in  some  places  far  from  shore. 

Coral  reefs  are  of  several  classes.  Those  which  are  separated  from 
the  land  by  a  somewhat  deep  channel  or  lagoon  are  barrier  reefs. 
Those  close  to  the  land  are  fringing  reefs.    Rudely  circular  reefs 


CORAL  REEFS  AND   ISLANDS  159 

inclosing  a  central  lagoon  are  atolls.  The  chief  importance  of  coral 
reefs  is  their  relation  to  navigation.  Atolls  frequently  afford  shelter 
to  vessels  in  distress.  Submerged  reefs,  however,  are  dangerous,  and 
long  barrier  reefs  may  hamper  commerce  seriously,  as  along  the  east 
coast  of  Australia. 

The  use  of  pink  or  red  coral  for  jewelry  leads  to  important  coral 
"fishing"  in  the  Mediterranean,  whence  much  of  the  product  goes  to 
India.  Most  of  the  natives  of  coral  islands  are  backward  in  civiliza- 
tion, because  of  the  limitation  of  their  resources. 


Questions 

1.  Why  is  agriculture  possible  on  a  limited  scale  in  Alaska,  and  not  in  the 
same  latitudes  in  Labrador,  Greenland,  and  Baffin  Land? 

2.  Why  is  Alaska  less  favorable  for  agriculture  than  Norway? 

3.  Why  is  the  climate  in  latitude  50°,  on  the  west  coast  of  South  America, 
less  favorable  for  farming  than  that  in  latitude  50°  on  the  west  coast  of  North 
America? 

4.  Why  are  isotherms  (Fig.  65)  affected  less  by  ocean  currents  in  the 
southern  hemisphere  than  in  the  northern? 

5.  Why  is  the  water  along  the  equator  in  the  Pacific  Ocean  warmer  toward 
the  western  border  of  the  ocean?  What  does  the  principle  involved  suggest  in 
regard  to  the  surface  temperatures  in  the  Gulf  of  Mexico? 

6.  Why  are  steamer  routes  across  the  Atlantic  farther  south  in  summer 
than  in  winter? 

7.  In  order  to  enter  a  shallow  harbor,  is  a  vessel  more  likely  to  have  to  wait 
for  flood  tide  at  the  time  of  neap  tides  or  at  the  time  of  spring  tides?     Why? 

8.  On  which  side  of  the  Gulf  Stream,  in  latitude  45°,  are  fogs  more  com- 
mon?    Why? 

9.  Are  fogs  more  likely  to  occur  over  a  warm  current,  or  over  a  cold  one? 
Why? 

10.  What  inference  might  be  drawn  from  the  fact  that  polyps  once  lived  within 
the  Arctic  Circle? 

11.  What  changes  in  geography  are  implied  by  the  fact  that  polyps  once  lived 
in  eastern  Wisconsin? 


CHAPTER  XIII 
THE  MATERIALS   OF  THE   LAND  AND  THEIR   USES 

General  Constitution 

The  mantle  rock.  The  loose  material  such  as  soil,  clay,  sand,  and 
gravel,  which  covers  most  of  the  land,  is  called  mantle  rock,  because 
it  forms  a  mantle  over  the  solid  rock  beneath.  Mantle  rock  varies 
in  thickness  from  a  few  inches  to  scores  or  even  hundreds  of  feet. 
It  is  formed  by  the  decay  and  breaking  up  of  solid  rock,  and  for  this 
reason  is  called  also  rock  waste. 

Soil  is  the  uppermost  part  of  the  mantle  rock,  which  serves  as  a 
source  of  food  for  plants.  It  varies  in  thickness  from  two  or  three 
inches  to  as  many  feet,  and  locally,  much  more.  Soil  consists  of  small 
particles  of  minerals,  usually  mixed  with  partly  decayed  vegetable 
matter  {humus) .  Both  mineral  and  organic  matter  are  necessary  parts 
of  a  good  soil,  but  their  proportions  vary  greatly.  In  color,  soil  may 
be  yellow,  dull  red,  gray,  brown,  or,  when  much  humus  is  present, 
black.     It  may  be  either  clayey  and  compact,  or  sandy  and  porous. 

In  order  to  support  plant  life,  soil  must  contain  both  air  and  water. 
Air  always  is  present  in  sufficient  amount,  unless  crowded  out  by 
excess  of  water,  as  in  some  swamp  soils.  On  the  other  hand,  the 
necessary  amount  of  water  may  be  lacking,  as  in  deserts.  Such  soils 
are  barren,  even  though  perfect  from  the  physical  and  chemical  stand- 
points. In  western  United  States,  large  areas  of  barren  land  need 
only  water  to  be  of  great  value. 

In  excavations,  as  for  cellars,  wells,  railway  cuts,  and  the  like, 
soil  may  be  seen  to  grade  down,  in  many  places,  into  subsoil,  which 
is  different  in  color  and  texture  from  the  soil  above.  In  most  places 
the  subsoil  is  much  thicker  than  the  soil,  though  it  may  be  absent 
altogether. 

Solid  rock.  Beneath  the  subsoil  is  solid  rock  (Fig.  74).  This 
extends  down  to  great  depths,  probably  even  to  the  center  of  the 
earth.  In  interior  United  States,  solid  rocks  may  be  seen  chiefly 
in  quarres,  mines,  along  the  courses  of  certain  rivers,  and  in  a  few 

160 


THE  SOIL  A  FUNDAMENTAL  RESOURCE 


i6i 


other  situations;  but  in  eastern  Canada,  in  western  Scandinavia, 
among  high  mountains  generally,  and  in  many  other  places,  they 
come  to  the  surface  over  large  areas.  Such  places  have  little  value 
from  the  standpoint  of  agriculture,  even  though  other  conditions  are 
favorable. 

Soils 

Importance  to  man.  Man  depends,  directly  or  indirectly,  on 
soil  for  most  of  that  which  he  eats  and  wears.  Products  of  the  soil 
furnish  the  principal  articles  of  commerce,  and  its  cultivation  con- 


Fig.  74.     Diagram  showing  soil  grading  into  solid  rock  beneath. 


stitutes  the  chief  basis  of  civilization.  These  relations,  too,  are  last- 
ing ones.  Whether  the  United  States  shall  in  the  future  support  a 
numerous,  well-to-do,  progressive  population,  or  a  sparse,  under-fed, 
and  non-progressive  one,  is  largely  a  question  of  whether  the  soil  of 
the  country  is  kept  abundant  and  fertile.  In  igoo,  more  than  a 
third  of  the  wage  earners  of  the  United  States  were  employed  in 
farming. 

The  Making  of  Soils 

We  have  seen  that  most  soils  are  formed  by  the  decay  and  break- 
ing up  of  solid  rocks.  All  changes  which  make  solid  rock  crumble  are 
processes  of  weathering.  The  weathering  of  rock  prepares  it  for 
transportation  by  wind  and  water. 

Chemical  processes.  The  oxygen,  carbon  dioxide,  and  water 
vapor  of  the  air  are  active  chemically.     The  meaning  of  chemical 


i62        MATERIALS  OF  THE  1.AND— THEIR  USES 


action  is  illustrated  by  the  rusting  of  iron.  Iron  rust  is  composed 
of  iron,  oxygen,  and  water.  Oxygen  and  water  from  the  air  enter 
into  chemical  combination  with  the  iron.  While  all  three  of  these 
substances  are  in  the  rust,  the  rust  does  not  look  like  any  one  of  them. 
The  union  of  oxygen  with  any  other  substance,  as  iron,  is  oxidation. 
The  union  of  water  with  another  substance  is  hydration.  Iron  rust 
is  therefore  oxidized  and  hydrated  iron. 

If  rusting  is  allowed  to  continue,  iron  is,  in  time,  "eaten  away"; 
that  is,  it  crumbles  to  pieces.  In  this  case,  as  in  many  others,  chemical 
change  produces  physical  change.  Many  rocks  contain  iron  which 
may  be  oxidized  and  hydrated.  When  such  rocks  are  exposed  to 
the  air,  therefore,  the  iron  in  them  is  changed  (rusted),  and  this  tends  to 
make  the  rock  crumble.  Other  chemical  changes  tend  to  produce  the 
same  result.  Some  of  the  substances  made  by  chemical  changes  in  the 
rocks  are  soluble,  and  if  they  are  dissolved  and  carried  away  by 
waters  passing  through  the  rock,  the  rock  from  which  they  are  taken 
is  left  more  porous,  and  weaker.  Some  rock-making  minerals  are 
soluble  without  chemical  change,  so  that  solution  is  one  of  the  most 

important  means  by 
which  rocks  are  made 
to  crumble,  and  by 
which  soils  are  formed. 
Mechanical  proc- 
esses, (i)  When 
water  freezes,  it  ex- 
pands about  one-tenth 
of  its  volume,  and  in 
doing  so  exerts  great 
force.  When  it  freezes 
in  rock  cavities  which 
it  nearly  fills,  it  acts 
like  a  wedge,  and  may 
pry  the  rock  apart  and 
break  off  pieces.  This 
process  of  rock-break- 
ing is  most  important 
when  there  is  abundant  moisture,  and  where  the  changes  of 
temperature  above  and  below  the  freezing  point  of  water  are  fre- 
quent. Rock-breaking  is  a  first  step  in  the  making  of  soil  from 
rock. 


Fig.  75.     Surface  of  bowlder  scaling  off  under 
changes  in  temperature.     (Tafif,  U.  S.  Geol.  Surv.) 


HOW  SOIL  IS  FORMED 


163 


(2)  Where  solid  rock  has  no  covering  of  loose  material,  as  on  many 
steep  slopes,  it  is  heated  by  day  and  cooled  by  night,  and  the  daily 
changes  of  temperature 
may  be  great.  Rocks  ex- 
pand when  heated  and 
contract  when  cooled,  and 
under  daily  heating  and 
cooling  their  surface  parts 
break  and  scale  off  (Fig. 
75).  The  breaking  of  cold 
glass  when  touched  with 
hot  water,  or  of  hot  glass 
when  touched  with  cold 
water,  involves  the  same 
principle.  The  shattering 
of  rock  by  heating  and 
cooling  is  very  common, 
particularly  in  high  moun- 
tains. Thus  the  upper 
part  of  many  a  mountain  is  covered  with  broken  rock  (Fig.  76),  so 
insecure  that  a  step  may  loosen  many  pieces  and  start  them  down  the 
mountain.     Great  piles  of  such  debris  (called  talus)  bury  the  bases 


Fig.  76.  Summit  of  Granite  Peak,  Wa- 
satch Mountains,  showing  broken  character 
of  the  rock.     (Church.) 


Fig.  77.    View  showing  long  talus  slopes.     (Russell,  U.  S.  Geol.  Surv.) 


i64        MATERIALS  OF  THE  LAND— THEIR  USES 


of  some  mountains  to  the  depth  of  hundreds  of  feet  (Fig.  77).  This 
debris  tends  to  decay,  gradually  forming  soil,  after  which,  if  other 
conditions  are  favorable,  the  slope  is  occupied  by  plant  life. 

(3)  The  growth  of  roots  in  cracks  in  the  rocks  may  enlarge  the 
openings,  and  so  help  to  break  the  rocks  (Fig.  78). 

(4)  The  multitudes  of  burrowing  animals  make  openings  in  the 
ground,  and  bring  large  quantities  of  loose  material  to  the  surface, 

where  it  is  exposed  to  air  and 
water,  and  is  by  them  changed  to 
soil. 

(5)  Rivers  wear  the  bottoms 
and  sides  of  their  channels,  and  so 
help  reduce  solid  rocks  to  fine 
material. 

(6)  Glaciers  grind  and  crush 
masses  of  rock  into  such  fine  mate- 
rial that  some  of  it  is  called  "rock 
flour."  Much  of  the  mantle  rock 
of  northeastern  United  States 
was  ground  up  by  ancient  glaciers 

(P-  251). 

(7)  In  many  dry  regions,  wind- 
driven  sand  wears  exposed  rocks  and  forms  much  fine,  loose  material, 
capable  of  becoming  soil. 

Classes  of  Soils 

In  the  paragraphs  which  follow,  the  term  soil  is  used  to  include 
the  subsoil  also,  where  the  distinction  between  them  is  not  important. 

Soil  which  remains  above  the  solid  rock  from  which  it  was  formed 
is  residual  soil  (Fig.  74).  On  the  other  hand,  transported  soil  has 
been  brought  from  its  place  of  origin  to  its  present  position  by  some 
of  the  agents  (wind,  water,  or  ice)  which  transport  materials  on  the 
surface  of  the  earth.  In  general,  transported  soils  are  richer  than 
residual  soils,  though  this  is  not  always  the  case. 

Residual  soils.  All  kinds  of  rock  decay,  and  the  decayed  rock, 
properly  weathered,  becomes  soil.  Residual  soils  vary  greatly  in 
fertility,  much  depending  on  the  character  of  the  parent  rocks. 
Thus  most  sandstones  weather  into  poor  soil.  Shales  produce  clay  soils 
of  greater  average  fertility,  but  in  some  cases  they  are  heavy,  and  hard 
to  work.    Limestone  soils  are,  as  a  class,  very  fertile,  but  if  their 


Fig.  78.  A  tree  growing  in  a 
crack  in  the  rock.  The  growth  of 
the  tree  widens  the  crack.  Sierra 
Nevada  Mountains,  California. 


CLASSES  OF  SOILS  165 

limey  constituents  are  dissolved  out,  as  they  may  be,  the  soil  is  less 
iertile. 

Transported  soils.  Transported  soils  are  much  less  uniform  in 
composition  and  texture  than  residual  soils.  In  many  cases  they 
represent  material  gathered  from  a  large  area,  and  are  entirely  unlike 
the  rocks  on  which  they  rest.  Sediment  transported  and  deposited 
by  rivers  is  alhivium,  and  soils  formed  on  alluvium  are  alluvial  soils. 
Such  soils  in  the  flood-plains  and  deltas  of  great  rivers,  when  not 
too  wet,  are  commonly  of  great  fertility.  The  rich  soil  of  the  great 
alluvial  fan  (p.  235)  of  the  Hwang-ho,  in  China,  supports  one  of 
the  densest  populations  in  the  world.  Ancient  civilizations  were 
confined  so  generally  to  rich  flood-plain  soils  that  the  period  before 
800  B.  c.  has  been  called  the  Fluvial  Period. 

Eolian  soils  are  formed  from  sand  or  silt  deposited  by  the  wind. 
Eolian  deposits  cover  large  areas  in  various  regions  (p.  202).  While 
the  sand  is  loose,  and  being  blown  about,  it  is  hardly  soil  and  offers 
little  chance  for  agriculture.  For  this  reason,  part  of  an  extensive 
area  of  sand-hills  in  western  Nebraska  has  been  set  aside  for  a  National 
Forest.  It  is  believed  that  certain  trees  which  can  get  along  with 
little  moisture  may  be  grown  there,  and  that  the  entire  sand  area, 
now  almost  worthless,  may  be  covered  with  a  profitable  forest. 
Large  areas  of  land  have  been  reclaimed  in  this  way  in  southwestern 
France. 

Wind  has  deposited  loess  in  certain  regions.  Loess  is  a  loam,  of 
buff  or  gray  color,  coarser  than  clay,  and  finer  than  sand.  Soils 
formed  from  loess  are  very  fertile  when  well  watered.  Some  of  the 
best  farming  lands  of  the  Rhine,  Danube,  and  other  European  river 
basins  have  loess  soils.  Similar  soils  occur  in  some  parts  of  the 
Mississippi  Basin,  particularly  along  parts  of  the  Mississippi  and 
Missouri  rivers. 

Before  the  Civil  War,  the  counties  of  Missouri  covered  with  loess  contained  a 
larger  percentage  of  slaves  than  most  of  the  rest,  and  grew  large  quantities  of 
tobacco.  The  loess-covered  counties  of  eastern  and  southeastern  Nebraska 
produce  most  of  the  corn,  wheat,  oats,  and  alfalfa  grown  in  the  state.  They  are 
settled  more  thickly,  and  have  more  improvements,  than  most  of  the  rest  of  the 
state. 

Much  of  the  mantle  rock  of  Canada  and  northern  United  States 
was  brought  to  its  present  position  by  the  great  ice-sheets  which  once 
covered  the  region  (p.  251).  This  material  is  called  drift.  Soil 
formed  from  drift  varies  much  in  character  and  fertility.     Some  of 


i66        MATERIALS  OF  THE  LAND— THEIR  USES 

it  is  too  sandy  and  some  is  too  stony  to  be  farmed  with  success,  but 
much  of  it  is  of  excellent  quality.  Since  the  glacial  drift  was  made 
not  very  long  ago  (as  geology  reckons  time)  by  the  grinding  up  of 
rocks  of  many  kinds,  the  soils  made  from  it  are  likely  to  contain  all 
the  mineral  elements  needed  for  plant  food. 

The  Removal  of  Soils 
Relation  of  gain  and  loss.  It  has  been  estimated  that  in  the 
United  States  it  may  take,  on  the  average,  10,000  years  to  form  a 
foot  of  residual  soil  (833  years  for  an  inch).  Slow  as  this  rate  is,  it  is 
faster  than  the  average  rate  at  which  soil  is  removed  by  surface 
waters,  winds,  etc.  If  soil  were  removed  faster  than  it  is  formed,  the 
land  would  in  time  be  without  soil,  as  it  is  now  in  some  places,  espe- 


Fig.  79.  View  in  the  Apennine  Mountains,  near  Florence.  Shows  the  shall 
low,  stony  soil  which  remains  after  the  loam  has  been  washed  away.  By  removing 
the  slight  protective  cover  of  vegetation,  the  sheep  promote  further  erosion. 
(Sketch  from  photograph  by  Willis.) 

cially  on  steep  slopes.  With  the  clearing  away  of  forests  and  the 
plowing  of  land  for  agriculture,  the  rate  of  soil  erosion  was  increased 
greatly,  and  it  now  exceeds  the  rate  of  soil  formation  over  large  areas. 
From  parts  of  the  Apennine  Mountains  (Fig.  79),  Dalmatia,  Pales- 
tine, and  China  (Fig.  80),  where  the  land  was  cultivated  for  centuries, 
the  soil  has  been  washed  away,  and  the  land  is  now  barren.  This 
shows  what  must  be  expected  in  some  parts  of  this  country,  if  the 
washing  away  of  soil  is  not  checked.     The  Mississippi  River  carries. 


LOSSES  FROM  SOIL  EROSION 


167 


on  the  average,  more  than  1,000,000  tons  of  the  richest  soil  matter 
into  the  Gulf  of  Mexico  every  day.  The  work  performed  each  year 
by  the  Missouri  River  in  transporting  material  toward  the  sea  is 
estimated  to  be  equivalent  to  275,000,000,000  ton-miles  (a  ton-mile 
is  a  ton  carried  a  mile).  All  the  railroads  of  the  United  States  carried 
218,800,000,000  ton-miles  of  freight  in  1909.  The  annual  loss  to  the 
country  from  the  washing  and  leaching  of  soil  is  estimated  at  some 


Fig.  80.  View  in  the  western  part  of  the  province  of  Chi-li,  China.  The 
erosion  has  been  aided  in  places  by  recent  deforestation.  (Willis,  Carnegie  Insti- 
tution.) 

$500,000,000.  Although  the  land,  even  of  eastern  United  States, 
has  been  cultivated  but  a  short  time  compared  with  that  of  Europe, 
yet  nearly  11,000,000  acres  once  farmed  have  been  abandoned.  More 
than  one-third  of  this  area  has  been  ruined  for  farming  by  the  erosion 
of  the  soil.  It  has  been  estimated  that  the  area  thus  ruined  would, 
if  covered  by  fertile  soil,  be  capable  of  supporting  a  population  greater 
than  that  of  any  one  of  the  twelve  least  populous  states.  Doubtless 
the  total  loss  to  the  country  from  the  partial  destruction  of  soil  is 
even  greater.  Nor  is  this  all.  ( i )  The  soil  carried  away  may  do  much 
harm  where  it  is  deposited.  (2)  Streams  which  carry  much  sediment 
deposit  some  of  it  in  their  channels,  thus  interfering  with  navigation. 
(3)  The  clogging  of  river  channels  also  helps  to  cause  floods.     (4)  Res- 


1 68 


MATERIALS   OF  THE  LAND— THEIR  USES 


ervoirs,  such  as  mill-ponds,  may  be  filled  with  sediment,  interfering 
with  manufacturing.  (5)  Streams  are  polluted,  interfering  seriously 
with  their  use  as  a  source  of  water  supply  for  cities,  and  making 
expensive  filtering  plants  necessary. 

Factors  controlling  soil  erosion.  Several  factors  influence  the 
rate  of  soil  erosion,  (i)  It  is  greater  on  steep  slopes  than  on  gentle 
ones.  Lands  in  the  southern  Appalachians  have  been  cleared  of 
forests  and  cultivated  where    slopes  are  so  steep  that  the  soil  was 

washed  away  in  eight 
n  or  ten  years,  and  the 
land  abandoned.  (2) 
It  varies  with  the 
amount  and  distribu- 
tion of  rainfall.  The 
more  the  rainfall  and 
the  more  rapidly  it 
falls,  the  more  rapid 
the  erosion  of  the  soil. 
The  greatest  storm  of 
a  year  may  wash  away 
more  soil  than  all  the 
other  rains  of  that 
year.  (3)  It  is  influ- 
enced by  the  presence  or  absence  of  vegetation,  and  in  the  case  of 
cultivated  land  by  the  kind  of  crop.  Bare  soils,  and  those  devoted 
to  widely-spaced  plants,  wash  faster  than  grass  lands  and  forest 
lands.  (4)  It  is  affected  by  the  texture  of  the  mantle  rock  and 
solid  rock.  (Which  would  favor  greater  wash,  compact  or  porous 
soil?     Compact  or  porous  material  below  the  soil?) 

Prevention  of  soil  erosion.  There  are  various  ways  of  reducing 
soil  erosion.  The  more  important  are  the  following:  (i)  Deep  and 
frequent  tillage  increases  the  power  of  the  soil  to  absorb  rain,  and 
so  reduces  the  amount  of  water  running  directly  off  over  the  surface. 
This  is  highly  desirable  apart  from  its  effect  on  erosion,  for  few 
places  have  water  enough  to  produce  maximum  crops.  (2)  Plowing 
and  planting  along  contours  (p.  16)  produce  little  depressions  and 
ridges  at  right  angles  to  the  slope.  These  tend  to  check  erosion 
(How?).  Plowing  up  and  down  a  slope,  on  the  other  hand,  increases 
erosion  (Why?).  (3)  On  steep  slopes,  wash  may  be  reduced  by  making 
a  series  of  terraces  or  benches.     Terracing  is  practiced  in  parts  of  the 


Fig.  81.     Terracing  in  western  North  Carolina. 
(Sketch  from  photograph  by  N.  C.  Geol.  Surv.) 


MINERAL  PLANT  FOODS 


169 


Piedmont  Plateau  (Fig.  81)  and  elsewhere  in  the  South,  and  in  many 
countries  of  Europe  and  Asia  (p.  312).  (4)  The  soil  should  be  kept 
covered  with  vegetation  as  much  as  possible  throughout  the  year. 
(5)  Grasses  tend  to  prevent  wash  in  several  ways  (How?).  (6)  On 
slopes  exceeding  18°  or  20°  in  steepness,  the  soil  is  protected  best 
by  trees  (Fig.  82),  and,  in  general,  such  land  should  be  devoted  to 
forests.  Lessening  soil 
erosion  is  one  of  the 
most  important  prob- 
lems of  conservation, 
and  it  depends  very 
largely  on  individual 
land-owners. 

Mineral  Plant  Foods 

Proper  care  of  the 
soil  calls  for  (i)  the 
prevention  of  erosion 
so  far  as  possible,  and 
(2)  the  keeping  in  the 
soil  of  the  mineral  mat- 
ters needful  for  plant 
food.  The  mineral  sub- 
stances of  importance 

are  phosphorus,  potassium,  calcium,  and  silicon,  though  a  few  others 
are  used  in  small  quantities.  Besides  these  mineral  substances,  plants 
need  carbon,  hydrogen,  oxygen,  and  nitrogen.  Different  crops  draw 
unequally  on  the  mineral  foods  of  the  soil,  and  when  one  crop  is  grown 
on  the  same  ground  year  after  year,  the  soil  may  become  poor  in  one 
or  more  of  these  foods,  and  its  productivity  be  reduced.  The  almost 
exclusive  cultivation  of  tobacco  injured  the  soil  in  parts  of  colonial 
Virginia.  This  helped  to  send  thousands  of  farmers  west  of  the 
Appalachian  Mountains  in  search  of  new  land.  Southern  Wisconsin 
was  primarily  a  wheat  region  from  the  1830's  to  the  1870's,  when 
the  diminishing  yields  and  the  competition  of  the  new,  rich  soils 
farther  northwest  led  to  the  raising  of  other  crops,  and  the  adoption 
of  better  methods  of  farming.  Where  crops  of  different  kinds  are, 
raised,  one  after  another  (rotation  of  crops),  the  soil  remains  ii> 
better  condition;  but  unless  the  essential  elements  taken  from  the 
soil  by  plants  are  returned  in  some  way,  its  fertility  must  diminish. 


Fig.  82.  View  showing  effect  of  roots  in  hold- 
ing soil.  San  Juan  Mountains,  Colorado,  near 
Silverton.     (Fairbanks.) 


I70        MATERIALS  OF  THE  LAND  —  THEIR  USES 

"Worn-out"  farms  are  common  in  the  South  and  East,  and  even  in 
parts  of  the  Upper  Mississippi  Basin.  Land  may  be  kept  from 
wearing  out  by  giving  it  the  elements  it  lacks,  that  is  by  fertilizing 
it.  In  some  parts  of  the  southeastern  states,  where  the  soil  was 
made  poor  by  the  long-continued  growth  of  cotton  or  tobacco,  no 
crops  are  grown  without  the  use  of  fertilizers. 

Natural  processes  tend  to  add  to  the  soil  the  substances  essential  to  plants, 
New  soil  is  formed  by  the  weathering  of  underlying  rocks  (p.  i6i),  and  ground- 
waters  bring  mineral  matter  in  solution  from  below,  which  they  may  deposit  neai 
the  surface,  enriching  the  soil.  In  most  cases,  these  processes  of  soil  renewal  and 
enrichment  fail  to  balance  the  loss  which  results  from  the  common  methods  of 
farming.  While  certain  natural  processes  tend  to  enrich  soils,  surface  and  under- 
ground waters  may  also  erode  and  leach  them  (p.  211),  thereby  reducing  their  pro- 
ductivity. 

The  supplies  of  most  of  the  elements  which  plants  need  are 
abundant  in  the  air,  the  ground-water,  or  the  soil.  Hydrogen  and 
oxygen  are  the  constituents  of  water,  and  oxygen  makes  one-fifth 
of  the  atmosphere.  The  air  contains  an  unlimited  supply  of  nitrogen, 
but  most  plants  get  their  nitrogen  from  compounds  of  that  substance 
in  the  soil  or  in  fertilizers  (p.  29).  Next  to  o.xygen,  silicon  is  the  most 
abundant  element  in  the  earth's  crust.  Most  rocks  contain  a  little 
calcium,  and  limestone  contains  much.  Carbon  is  derived  from  the 
carbon  dioxide  of  the  air.  Potassium  is  a  constituent  of  many  common 
rocks,  and  there  are  large  deposits  of  potassium  compounds  in  various 
places.  Wood  ashes  contain  potassium,  and  for  this  reason  they  are 
good  for  land. 

Unlike  the  foregoing,  phosphorus  is  a  relatively  rare  element,  and 
already  the  original  amount  in  the  soil  has  been  diminished  seriously 
in  many  parts  of  the  United  States.  Guano,  chiefly  from  islands  off 
the  west  coast  of  South  America,  is  an  important  source  of  supply, 
though  little  is  imported  into  the  United  States.  The  bones  of  do- 
mestic animals  are  a  second  source,  and  the  manufacture  of  phosphate 
fertilizer  is  an  important  industry  at  the  great  slaughtering  centers. 
The  bones  of  buffaloes,  killed  in  great  numbers  years  ago,  have  been 
gathered  up  by  the  train-load  from  the  western  plains  and  used  in  the 
same  way.  Enormous  quantities  of  phosphorus  are  now  lost  in  the 
sewage  of  great  cities,  and  in  the  leaching  of  farm  manure.  This 
phosphorus  should  be  returned  to  the  soil,  so  far  as  possible.  Some 
European  countries  are  far  ahead  of  the  United  States  in  this  matter. 
Finally,  the  United  States  possesses  the  greatest  known  deposits  of 
phosphate  rock  (rock  containing  much  phosphorus),  and  because 


DISTRIBUTION  OF  SOILS  IN  UNITED   STATES      171 

phosphorus  is  to  be  a  critical  factor  in  the  fertility  of  soil,  these  de- 
posits constitute  one  of  the  most  important  mineral  possessions  of  the 
nation.  In  the  Southeast,  there  are  deposits  in  South  Carolina,  Flor- 
ida, Tennessee,  and  Arkansas.  The  first  three  of  these  states  furnish 
nearly  all  the  phosphate  rock  now  mined  in  the  United  States.  In 
addition,  there  are  far  greater  deposits  in  Idaho,  Wyoming,  Utah, 
and  Montana.  There  is,  unfortunately,  much  waste  of  the  poorer 
phosphate  rock  in  mining  —  material  which,  if  saved,  would  be  of 
great  value  in  the  future.  Unfortunately  for  the  United  States,  too, 
increasingly  large  amounts  of  phosphate  are  being  exported. 

It  is  not  to  be  inferred  from  the  above  discussion  that  fertility  of  soil  is  deter- 
mined solely  by  its  chemical  composition.  Its  productivity  is  influenced  also  by 
(i)  its  physical  condition  (coarseness,  fineness,  etc.),  (2)  its  water  content,  (3)  the 
organic  matter  (humus,  etc.)  which  it  contains,  (4)  the  minute  organisms  (especially 
bacteria)  at  work  in  it,  (5)  the  presence  of  toxic  bodies  (the  accumulated  e.xcreta  of 
plants),  and  by  other  factors.  Furthermore,  the  yields  obtained  from  a  given  soil 
are  affected  greatly  by  (i)  the  quality  of  seed  sown,  (2)  the  effectiveness  of  cultiva- 
tion, and,  in  many  cases,  by  such  things  as  (3)  harmful  insects,  (4)  plant  diseases, 
and  (5)  weather  conditions.  The  reduced  yields  of  many  long-cropped  soils 
probably  are  due  in  part  to  causes  other  than  the  impoverishment  of  the  mineral 
elements  of  plant  food. 

General  Distribution  and  Use  of  Soils  in  the  United  States 

The  principal  physiographic  provinces  of  the  United  States  are  shown  in  Fig 
83.     Since  the  settlement  and  development  of  these  provinces  have  been  influenced 
profoundly  by  the  topography  of  the  land  and  the  character  of  the  soil,  the  larger 
provinces  may  be  considered  briefly. 

The  Atlantic  and  Gulf  Coastal  Plains.  Much  of  the  Coastal  Plain  is  less  than 
100  feet  above  sea-level,  though  some  parts  of  it  are  considerably  higher.  The 
underlying  rocks  are  imperfectly  cemented  gravels,  sands,  clays,  marls,  and  lime- 
stones. Along  the  coast  there  are  extensive  marshes,  where  most  of  the  soil  is  too 
wet  to  cultivate.  The  draining  of  these  swamps  has  been  begun,  as  for  example 
on  the  delta  and  lower  flood-plain  of  the  Mississippi,  and  when  it  is  completed  their 
rich  soils  will  support  many  people  (p.  301).  Elsewhere,  the  soils  of  the  Coastal 
Plain  present  great  variety.  Over  the  marls  and  limestones  they  are  fertile,  and 
over  the  sands,  gravels,  and  clays,  they  are  much  less  productive.  JSIany  sandy 
tracts,  as  in  parts  of  southern  New  Jersey,  have  remained  wooded  and  sparsely 
settled  to  the  present.  In  the  Carolinas  such  belts,  called  "barrens,"  long  helped 
to  separate  the  life  of  the  tidewater  country  from  that  of  the  Piedmont  Plateau. 
In  contrast  with  the  sandy  areas,  the  bottom  lands  of  the  rivers,  where  not  too  wet. 
and  the  belts  of  limestone  soils  are  the  garden  spots  of  the  South.  Here  most 
cotton  was  grown  before  the  Civil  War,  and  most  slaves  were  owned  (p.  325). 
Here  the  negro  population  is  densest  to-day.  It  probably  is  true  that  the  rich  soila 
of  many  parts  of  the  Coastal  Plain,  and  the  genial  climate  of  the  South,  were  re- 
sponsible for  the  continuance  of  slavery  in  the  United  States  to  the  time  of  the 
Civil  War. 


172        MATERIALS  OF  THE  LAND— THEIR  USES 

The  New  England  Hills.  There  is  no  continuous  coastal  plain  in  New 
England.  The  most  important  lowlands  have  developed  on  weak  rocks  in  the 
Connecticut  Valley,  about  Narragansett  Bay,  and  around  Boston.  On  these  low- 
lands the  early  history  of  Connecticut,  Rhode  Island,  and  Massachusetts  centered. 
To-day,  the  Boston  Basin  contains  about  half  the  people  of  Massachusetts,  and 
one-fourth  those  of  all  New  England.  Apart  from  these  lowlands,  most  of  New 
England  is  hilly.  IMuch  of  its  glacial  soil  is  thin  and  poor,  and  in  many  places 
stony.  It  has  been  estimated  that  in  some  parts  it  took,  on  the  average,  one 
month  for  a  man  to  remove  the  stones  from  each  acre  of  glacial  drift,  to  get  it  ready 


Fig.  83.  ]Map  showing  the  principal  physiographic  subdivisions  of  the  United 
States. 

for  farming.  Many  of  the  early  settlements  were  made  in  areas  of  stratified  drift 
(p.  266),  where  the  bowlders  were  fewer  and  the  land  flatter. 

The  unfavorable  soils  and  the  harsh  climate  prevented  a  high  development 
of  agriculture  in  New  England,  which  was  without  a  single  staple  crop  for  export, 
such  as  colonial  Virginia  had  in  tobacco,  and  South  Carolina  in  rice  and  indigo. 
By  the  close  of  the  seventeenth  century,  more  than  half  the  people  of  New  England 
were  engaged  in  industries  other  than  agriculture,  and  it  is  said  also  that  more  than 
half  the  time  of  the  farmers  was  given  to  non-agricultural  work.  For  two  centuries 
the  life  of  New  England  was  dominated  by  industries  centering  in  the  ocean — 
chiefly  fishing,  shipbuilding,  and  the  carrymg  trade.  Later,  manufacturing  became 
the  leading  interest. 

Crude  methods  of  agriculture  in  early  days  led  to  the  exhaustion  or  partial 
exhaustion  of  many  lands  which  were  originally  good  for  farming.  When  the  lands 
ceased  to  produce  good  crops  they  were  deserted.  Much  has  been  written  and  said 
of  the  abandoned  farms  of  New  England,  but  in  recent  years  many  of  them  have 
been  brought  under  cultivation  again,  and  with  the  improved  methods  of  to-day 
they  are  producing  satisfactory  retiums.    It  seems  certam  that  many  of  the 


DISTRIBUTION  OF  SOILS  IN  UNITED  STATES      173 

abandoned  farms  will  be  reclaimed.  Much  of  the  rough,  infertile  upland,  however, 
probably  can  be  used  to  best  advantage  in  the  future  for  forests. 

The  Piedmont  Plateau.  The  Piedmont  Plateau  has  an  elevation  varying 
from  250  or  300  feet  at  its  eastern  edge,  to  about  1,000  feet  in  places  along  its 
western  margin.  The  higher  lands  have  a  rather  poor,  residual  soil,  but  many  of 
the  valleys  have  rich,  alluvial  bottoms. 

The  Appalachian  Mountains.  The  soils  of  the  larger  valleys  are  fairly  fertile. 
This  was  strikingly  true,  originally,  of  the  limestone  soils  of  the  Great  Appalachian 
Valley,  which,  under  various  names,  extends  from  Georgia  to  New  York.  This 
great  valley  was  one  of  the  first  areas  west  of  the  Blue  Ridge  to  be  settled,  and  it 
soon  became  an  important  grain  producing  section.  During  the  Civil  War,  the 
Confederate  armies  drew  large  quantities  of  supplies  from  its  fertile  fields. 

The  upper  slopes  of  these  mountains  are  steep,  and  covered  with  soil  which 
washes  easily  when  the  forest  is  removed.  A  National  Forest  is  to  be  established 
in  the  southern  Appalachians,  and  the  steeper  land  devoted  permanently  to  forestry. 
In  the  future,  the  country  must  look  to  Appalachian  forests  for  much  of  its  supply 
of  hardwood. 

The  Cumberland-Alleghany  Plateau.  The  surface  of  this  plateau  is  much 
dissected  by  valleys  cut  in  the  nearly  horizontal  layers  of  rocks.  In  general, 
relatively  level  land  and  fertile  soil  are  found  only  in  the  valley  bottoms.  The  hills 
have  steep  slopes,  and  their  soils  are  infertile.  Except  where  mineral  resources 
have  attracted  settlers,  the  plateau  is  sparsely  settled. 

Lake  and  Prairie  Plains.  Most  of  the  surface  of  this  area  is  covered  with 
glacial  soil  (Fig.  170),  the  composition  of  which  is  influenced  greatly  by  the  nature 
of  the  underlying  rocks.  Thus  in  Michigan  and  Wisconsin  there  are  large  areas 
of  sandy  drift  over  sandstone,  where  attempts  at  farming,  following  the  removal  of 
the  pine  forests,  have  met  with  little  success.  There  are  also  hilly  belts  (moraines, 
p.  258)  in  the  northern  part  of  the  area,  where  the  stony  soil  is  used  largely  for  wood- 
lots  and  pasturage.  There  is  also  much  marsh  land,  unfit  for  agriculture  until 
drained.  In  general,  however,  the  soils  of  this  region,  especially  the  prairie  soils 
between  the  Missouri  and  Ohio  rivers  on  the  south  and  southwest  and  the  Great 
Lakes  on  the  north,  are  of  great  fertility.  No  other  equal  area  in  the  United  States 
is  so  important  agriculturally  (Fig.  257).  Iowa,  Illinois,  Ohio,  and  Indiana,  in  the 
order  named ,  are  the  first  four  states  in  the  percentage  of  improved  land  to  total  area. 

The  prairies  generally  were  avoided  by  the  first  settlers,  who  regarded  the 
absence  of  trees  as  evidence  of  poor  soil.  Even  after  their  fertility  was  known,  the 
larger  prairies  were  not  settled  far  back  from  the  main  streams  until  the  building 
of  railroads  provided  means  of  transportation. 

The  Great  Plains.  The  surface  of  this  province  rises  from  an  elevation  of 
about  1,000  feet  at  the  east,  to  more  than  5,000  feet  at  the  west.  Most  of  the 
region  has  a  deep  and  rich  soil.  At  the  north,  the  soil  is  of  glacial  origin  (Fig.  1 70) ; 
farther  south  it  is  (i)  partly  alluvial,  having  been  spread  widely  by  depositing  rivers 
flowing  eastward  from  the  Rocky  Mountains,  (2)  partly  residual,  and  (3)  consider- 
able areas  in  the  eastern  part  of  the  tract  are  covered  with  loess  (p.  165).  The 
eastern  part  of  the  area  is  very  productive,  but  the  western  part  has  too  little  rain 
for  ordinary  farming.  Here  agriculture  must  depend  on  (i)  irrigation,  which  is 
possible  over  small  areas,  (2)  "dry  farming"  (p.  329),  and  (3)  the  cultivation  of 
drought-resisting  plants,  such  as  durum  wheat  and  kafiir  corn.  Over  large  areas 
grazing  probably  will  continue  to  be  the  chief  interest  (p.  329). 


174 


MATERIALS  OF  THE  LAND— THEIR  USES 


The  Rocky  Mountains  and  Western  Plateaus.  In  the  different  parts  of 
tliis  great  region  all  kinds  of  rocks  are  found,  in  all  sorts  of  positions.  The  soils 
vary  as  greatly  as  the  rocks,  both  in  origin  and  composition.  Glacial  soils  are  found 
at  the  north,  and  throughout  the  region  in  many  mountain  valleys.     Great  areas 


LEGEND 

19«^^  Absolute  Forest  Land 
2«K53IntermediaTe  between  Agricuitu 

and  Forest  Land 

5l«I^HAgricultural  Land 
2611^^^ Grazing  Land 

■»:i«l I  Barron  Land 

I0d»  Total 


P'ig.  84.     Map  showing  the  best  use  to  which  it  is  thought  the  land  through- 
out North  America  may  be  put.     (Zon,  U.  S.  Forest  Service.) 


BUILDING  STONES  AND  CLAYS  175 

of  alluvial  soil  fringe  the  bases  of  many  of  the  mountains,  where  witljering  streams 
from  the  uplands  have  deposited  their  sediment.  Some  of  these  deposits  have  a 
thickness  of  hundreds  and  even  thousands  of  feet.  The  steep  slopes  are  flanked 
also  by  great  piles  of  talus  (p.  163),  most  of  which  do  not  support  much  plant  life. 
Where  the  mountain  slopes  are  not  too  steep,  there  are  residual  soils,  and  these 
also  cover  great  areas  of  the  plateaus. 

Over  most  of  the  region,  systematic  tillage  of  the  soil  has  not  been  possible 
because  of  (i)  too  great  height,  (2)  the  steepness  of  the  slopes,  or  (3)  lack  of  ade- 
quate rain.  Most  of  the  land  is  therefore  best  suited  to  grazing,  and,  especially  in 
the  mountains,  to  forestry.  Irrigation  is  making  agriculture  possible  in  many 
rather  small  areas  (p.  293),  especially  in  valleys  and  on  other  lowlands.  In  some 
such  places,  there  is  a  dense  population.  Nowhere  else  in  the  world  is  fruit-raising 
carried  on  more  intelligently  or  with  better  results,  and  probably  nowhere  else  in 
the  world  has  farm  land  sold  at  such  high  prices.  Small,  choice  orchards  have  been 
sold  at  $4,000  and  $5,000  per  acre,  and  prices  half  as  high  are  not  rare. 

The  Pacific  Ranges.  As  farther  east,  the  soils  of  the  mountain  slopes  can 
be  used  best  for  forests,  for  which,  except  at  the  south,  there  is  enough  rain.  Among 
the  mountains  there  are  many  fertile  valleys  with  glacial  or  alluvial  soils,  and 
between  the  ranges  are  the  great  waste-filled  valleys  of  the  Willamette  River  and  of 
central  California.  The  rich,  alluvial  soils  of  the  latter  probably  have  given  the 
state  larger  returns  than  its  gold  mines.  In  the  southern  part  of  the  province,  the 
value  of  even  the  best  soil  depends  on  irrigation,  and  unfortunately  there  is  water 
enough  to  irrigate  only  about  one-tenth  of  the  land.  Irrigated  land,  with  groves 
of  oranges  or  lemons,  sells  for  very  high  prices,  while  non-irrigable  land  is  worth 
but  little.  Toward  the  north,  with  increase  of  rainfall  and  with  lower  tempera- 
tures, the  necessity  of  irrigation  is  less. 

Fig.  84  shows,  in  a  general  way,  the  best  use  to  which  it  is  thought  the  land 
throughout  North  America  may  be  put,  and  serves  to  illustrate  many  of  the  larger 
points  stated  in  the  preceding  paragraphs. 


Mineral  Products  and  Their  Uses 
Building  Stones  and  Clay 

Building  stones.  The  principal  building  stones  are  granite, 
limestone,  marble,  slate,  and  sandstone,  though  not  all  rocks  of  these 
kinds  are  useful  for  building.  The  strength  of  the  rock,  its  color,  ease 
of  splitting  and  dressing,  and  durability  all  enter  into  the  problem. 
Not  all  good  stone  is  available,  for  much  is  too  far  from  a  market. 
Cement  is  taking  the  place  of  building  stone  to  a  very  large  extent. 

Granite  is  distributed  widely  in  the  United  States,  and  is  quarried 
in  a  large  way  in  several  of  the  Atlantic  States.  Limestone  is  quarried 
in  many  states,  largely  for  local  use.  From  a  few  famous  quarries, 
such  as  those  at  Bedford,  Indiana,  it  is  shipped  to  all  parts  of  the 
United  States.  Much  limestone  is  burned  for  lime,  and  much  is 
used  for  mortar,  cement,  railroad  ballast,  etc.    The  growth  of  the 


176        MATERIALS  OF  THE  LAND— THEIR  USES 

cement  industry  has  been  remarkably  rapid.  In  1890,  the  United 
States  produced  less  than  350,000  barrels  of  Portland  cement;  in 
191 1,  more  than  79,500,000  barrels.  Much  marble  is  used  as  an 
ornamental  building  stone.  Until  recently,  it  has  been  quarried  on 
a  large  scale  only  in  the  East.  Vermont  supplies  about  four-fifths  of 
all  the  marble  used  in  the  United  States  for  ornamental  work,  but 
Colorado  promises  to  become  a  great  producer. 

Slates  are  used  chiefly  as  roofing  material,  but  also  for  various 
other  purposes.  The  production  of  slate,  like  that  of  marble,  is 
confined  largely  to  the  East,  and  is  most  important  in  Pennsylvania, 
Vermont,  and  New  York.  Sandstone  is  used  for  buildings,  bridges, 
and  other  purposes.  It  is  distributed  widely  in  many  states,  so 
that  many  small  quarries  serve  local  needs.  A  few  popular  kinds 
of  sandstone,  such  as  the  brownstone  from  Pennsylvania  and  the 
vicinity  of  New  York  City,  have  wider  markets. 

Gypsum  is  used  extensively  for  building-plaster  and  certain 
cements.     It  is  used  also  as  a  land  fertilizer,  and  in  other  ways. 

Clays  and  clay  products.  Clays  have  a  wider  distribution 
than  most  other  economic  rock  materials,  and  are  used  in  making 
many  things.  Among  these  are  pottery  of  various  grades,  tiles, 
terra  cotta,  brick,  and  Portland  cement  (made  from  a  mixture  of 
clay  and  lime  rock).  Every  state  produces  clay  products,  Ohio, 
Pennsylvania,  New  Jersey,  and  Illinois  leading  in  the  order  named. 
The  total  value  of  the  products  of  the  clay-working  industries  of  the 
country  exceeded  $162,000,000  in  1911. 

Substitution  of  mineral  products  for  wood.  Brick,  stone, 
and  cement  are  being  substituted  more  and  more  for  wood  in  build- 
ings, sidewalks,  bridges,  piers,  etc.  This  is  highly  desirable,  because 
these  materials  are  (i)  more  durable,  (2)  less  liable  to  fire,  and  (3) 
their  use  lessens  the  drain  on  the  forests. 

Mineral  Fuels 
Coal.  After  soil,  coal  is  the  most  important  of  the  mineral 
resources.  Together  with  iron,  which  is  next  in  importance,  it  has 
made  possible  the  extraordinary  industrial  development  of  the 
United  States.  Germany  and  England  also  have  become  great  manu- 
facturing nations  largely  because  of  their  extensive  deposits  of  coal 
and  iron.  The  United  States  has  more  and  better  coal  than  any  other 
country,  so  far  as  known.  Fig.  85  shows  the  general  distribution 
of  its  coal  fields.     Their  combined  area  is  about  500,000  square  miles, 


COAL  SUPPLY  OF  THE  UNITED   STATES 


177 


01  about  16  per  cent  of  the  area  of  the  country.  Their  wide  distribu- 
tion is  a  matter  of  great  importance,  since  the  largest  item  in  the  cost 
of  coal  is  the  cost  of  transportation.  The  amount  of  coal  in  the 
United  States  at  the  beginning  of  191 1  was  estimated  at  more  than 
3,062,800,000,000  tons.  About  one-third  of  this,  however,  is  accessi- 
ble only  with  difficulty,  and  by  no  means  all  of  it  is  of  good  quality. 


Fig.  85.     Map  showing  general  distribution  of  coal  fields  in  the  United  States. 
(U.  S.  Geol.  Surv.) 


It  is  estimated  that  more  than  99  per  cent  of  the  original  supply  of 
coal  in  the  United  States  is  still  in  the  ground. 

The  mining  of  coal  in  the  United  States  began  to  be  important 
about  the  middle  of  the  last  century,  and  the  output  has  nearly 
doubled  each  decade  since.  The  496,000,000  tons  mined  in  191 1 
was  about  V^?  of  all  mined  to  the  end  of  that  year.  If  the  output 
should  continue  to  increase  at  the  same  rate,  the  entire  known  supply 
would  be  exhausted  in  less  than  150  years.  For  various  reasons, 
however,  our  supply  of  coal  will  last  much  longer  than  this.  Never- 
theless, it  is  highly  desirable  (i)  to  avoid,  so  far  as  possible,  the 
waste  of  coal;  (2)  to  substitute  water  power  for  steam  power  (gen- 
erated by  the  burning  of  coal)  wherever  practicable;  and  (3)  to  use 
coal  in  the  most  efficient  way  possible.  The  waste  in  mining  coal 
has  amounted  to  about  50  per  cent  of  the  quantity  produced;   that 


178        MATERIALS  OF  THE  LAND  — THEIR  USES 


is,  about  250,000,000  tons  were  wasted  in  this  way  in  191 1.  This 
is  more  coal  than  was  mined  in  the  United  Kingdom  (the  second 
coal-producing  country)  in  1905.  Much  unburned  coal  passes  off 
as  smoke.  The  average  steam  engine  does  not  develop  into  power 
more  than  6  to  10  per  cent  of  the  heat  energy  of  the  coal.  In 
making  electric  light  from  coal,  only  a  small  part  of  one  per  cent 
of  the  energy  of  the  coal  is  utilized.      Much  of  this  waste  can  be 


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lis,.  86.  Map  showing  general  distribution  of  petroleum  and  natural  gas 
fields  (the  black  areas)  of  United  States.     (Day,  U.  S.  Geol.  Surv.) 

avoided,  and  some  progress  in  this  direction  has  been  made  already. 
One  effect  of  the  burning  of  large  quantities  of  coal  is  to  increase 
the  amount  of  carbon  dioxide  in  the  air  (p.  30).  Indeed,  it  has 
been  estimated  that  the  amount  may  be  doubled  in  this  way  in  the 
next  1,500  years.  It  will  be  remembered  (p.  31)  that  this  probably 
would  make  the  climate  much  milder. 

Pennsylvania,  West  Virginia,  Illinois,  and  Ohio  lead  in  mining 
coal.  They  have  produced  about  3^  of  all  the  coal  mined  in  the 
United  States. 

Petroleum.  Petroleum  was  discovered  in  large  quantities  in  west- 
ern Pennsylvania  in  1859.  The  field  which  includes  this  original  area 
extends  from  New  York  to  Tennessee  (Fig.  86),  and  has  produced 
more  petroleum  than  any  other.     The  output  is  now  decreasing, 


SUPPLY  OF  IRON  IN   THE    UNITED    STATES       179 

hovrever.  Most  of  the  petroleum  of  this  field  is  of  high  grade.  The 
large  Ohio-Indiana  field  was  the  second  to  come  into  use  (about  1885). 
Most  of  the  others  are  of  recent  development.  In  191 1,  California 
produced  most  petroleum,  and  Oklahoma  and  Illinois  ranked  second 
and  third.  The  total  output  of  the  country  during  this  year  was 
more  than  220,000,000  barrels.  Since  i860,  as  much  petroleum  has 
been  produced  each  nine  years  as  in  all  preceding  years,  and  should 
this  rate  continue,  the  supply,  so  far  as  it  can  be  estimated  in  known 
fields,  would  be  exhausted  by  about  1935.  Should  the  present  output 
continue  without  increase,  the  calculated  supply  will  last  until  about 
the  year  2000. 

Crude  oil  is  used  for  fuel,  for  the  prevention  of  dust  on  roads,  and 
for  some  other  purposes.  From  it  various  oils  are  manufactured 
for  lighting  and  lubricating  purposes,  and  many  by-products  are 
obtained.  In  view  of  the  probable  early  exhaustion  of  the  supply, 
petroleum  should  be  used  only  for  those  purposes  for  which  it  is 
best  adapted.  Its  most  essential  use  is  for  the  making  of  oils  for 
lubricating  the  bearings  of  all  kinds  of  machinery.  For  this  purpose, 
no  satisfactory  substitute  is  known.  On  the  other  hand,  the  use  of 
petroleum  as  fuel  in  locomotives  and  for  the  development  of  power 
in  factories  is  in  most  places  unnecessary,  and  should  be  discouraged. 

Natural  gas.  Natural  gas  is  the  most  perfect  fuel.  So  far  as 
known,  the  United  States  has  a  greater  supply  than  any  other  nation, 
and  it  occurs  in  more  than  half  the  states  (Fig.  86).  It  is  believed, 
however,  that  the  natural  gas  now  known  will  be  exhausted  within 
the  next  twenty-five  or  thirty  years.  In  spite  of  this,  and  in  spite  of 
its  great  value,  enormous  quantities  (estimated  at  1,000,000,000 
cubic  feet  daily)  are  allowed  to  escape  from  the  ground  unused.  A 
large  part  of  this  waste  can  be  prevented. 

Metals 

Iron.  Some  iron  was  mined  in  this  country  in  the  colonial 
period.  The  production  was  unimportant,  however,  till  1850.  Since 
then  it  has  increased  rapidly,  so  that  the  output  during  the  decade 
ending  with  1909  amounted  to  52.6  per  cent  of  all  the  iron  ore  that  has 
been  mined  in  the  United  States. 

It  was  estimated  recently  that  the  available  iron  ore  (that  usable 
under  existing  conditions)  in  the  United  States  amounts  to  nearly 
4,800,000,000  long  tons  (a  long  ton  is  2,240  lbs.),  and  that  in  addition 
there  are  low  grade  ores,  part  or  all  of  which  will  be  useful  in  the  future, 


i8o        MATERIALS  OF  THE  LAND— THEIR  USES 

amounting  to  more  than  75,000,000,000  long  tons.  Like  coal,  iron 
ore  is  distributed  widely  (Fig.  87),  but  by  far  the  most  important 
deposits  of  our  country  are  in  the  Lake  Superior  region,  especially 
in  northern  Michigan  and  Minnesota.  This  district  contains  about 
73  per  cent  of  the  available  ore  of  the  United  States,  and  about  95 
per  cent  of  the  low-grade  reserve.  It  had  produced,  to  the  end  of 
191 1,  more  than  530,000,000  long  tons  of  iron  ore — considerably  more 


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Fig.  87.  Map  showing  general  distribution  of  iron  ore  in  the  United  States 
Some  of  the  smaller  areas  contain  more  and  richer  ore  than  the  larger  ones. 

than  half  the  total  amount  produced  in  the  United  States.  In  recent 
years  it  has  furnished  about  80  per  cent  of  the  entire  output  of  the 
country.  In  19 10,  the  United  States  produced  more  than  56,800,000 
long  tons  of  iron  ore — nearly  half  the  world's  production  for  the  year. 
In  191 1,  however,  the  output  was  only  about  41,000,000  tons. 

If  the  iron  ores  of  the  United  States  continue  to  be  mined  at  the 
increasing  rate  of  the  last  few  decades,  the  known  deposits  of  high 
grade  will  all  be  mined  in  about  ninety  years.  Several  considerations, 
however,  make  it  certain  that  the  supply  of  ore  will  last  much  longer. 
Furthermore,  iron,  unlike  coal,  can  be  used  again  and  again.  For 
example,  old  rails  are  made  over  into  new  ones  or  into  other  things. 
The  great  problem  in  conserving  the  supply  of  iron  is  therefore  to 
use  it  again  and  again,  keeping  the  stock  as  nearly  intact  as  possible. 
There  is  little  waste  of  iron  ore  in  mining. 


COPPER,    GOLD,   AND   SILVER  i8i 

Copper.  The  existence  of  copper  on  the  southern  shore  of 
Lake  Superior  (Keweenaw  Point)  was  known  to  the  Indians  at  an 
early  date.  As  late  as  1845,  however,  the  entire  output  in  the  United 
States  amounted  to  only  100  tons  a  year,  and  not  till  1867  did  copper 
begin  to  be  used  in  large  amounts.  Its  use  has  increased  rapidly  in 
recent  years,  about  550,000  tons  being  produced  in  igii.  Nearly 
three-fifths  of  the  entire  amount  produced  in  the  United  States  have 
been  mined  in  the  last  ten  years.  Michigan,  long  the  leading  copper 
state,  is  now  outranked  by  Arizona  and  Montana.  Some  nine  other 
states,  most  of  them  in  the  West,  produce  copper,  several  of  them 
in  large  amounts. 

Copper  ores  are  scattered  so  widely,  and  are  so  irregular  in  their 
occurrence,  that  the  supply  has  not  been  estimated  accurately. 
It  is  thought,  however,  that  the  known  copper  ore,  usable  at  existing 
prices,  will  be  exhausted  in  Michigan  in  fifteen  or  twenty  years,  and 
in  Montana  and  Arizona  in  even  less  time.  Should  the  value  of  copper 
increase,  lower  grade  ore  could  be  used.  Even  now,  at  the  Michigan 
mines,  only  twenty-two  pounds  of  copper  are  obtained,  on  the  average, 
from  each  ton  of  ore.  New  discoveries  of  copper  are  made  from  time 
to  time,  and  for  this  and  other  reasons,  copper  ore  will  last  much 
longer  than  the  time  suggested  above. 

Copper  is  used  chiefly  for  making  wire  and  brass.  These  uses 
involve  little  unavoidable  waste,  and  the  same  copper  may  be  used 
repeatedly. 

Gold.  The  production  of  gold  was  unimportant  in  the  United 
States  until  after  its  discovery  in  California  in  1848.  The  leading 
gold-producing  states  are  California,  Colorado,  and  Nevada.  Each 
produces  about  1,000,000  ounces  (an  ounce  is  worth  about  $20)  of 
gold  per  year.  Alaska  is  also  a  heavy  producer.  The  amount  of  gold 
which  remains  to  be  mined  cannot  be  estimated.  It  already  is  practi- 
cable to  mine  very  low  grade  ore.  In  some  cases,  for  example,  a  ton 
of  ore  is  mined  and  milled  to  recover  one-eighth  of  an  ounce  of  gold. 
Gold  is  used  chiefly  as  coin  and  bullion,  and  in  the  arts.  Most  of  its 
uses  involve  little  waste  or  loss  of  the  gold  itself.  Even  were  the 
supply  used  up,  the  loss  would  be  much  less  serious  than  that  of  coal 
or  iron. 

Silver.  Neither  the  amount  nor  the  duration  of  the  silver 
deposits  of  the  United  States  can  be  estimated.  Nevada,  Montana, 
and  Utah  are  (19 10)  the  leading  silver-producing  states,  followed 
by  Colorado  and  Idaho.     Like  gold,  silver  is  used  chiefly  for  coin  and 


i82        MATERIALS  OF  THE  LAND  — THEIR  USES 

in  the  arts.     Its  use  in  photography  is  an  interesting  and  a  rapidly 
increasing  one.     In  general,  there  is  little  waste  or  loss  in  its  use. 

Lead  and  zinc.  Lead  was  known  to  the  Indians  of  the  Missis- 
sippi Valley  before  the  coming  of  the  whites,  but  the  deposits  of 
the  region  were  not  worked  effectively  until  the  early  1820's,  when 
a  period  of  great  activity  in  mining  began.  This  culminated  in 
Illinois  and  Wisconsin  about  1845.  During  the  next  few  years 
many  of  the  miners  went  to  the  iron  fields  of  Lake  Superior,  and 
to  the  gold  fields  of  California.  Lead  was  discovered  later  in 
various  western  states,  in  many  places  in  association  with  silver. 
Missouri  is  the  leading  lead-producing  state,  followed  by  Idaho  and 
Utah. 

The  known  supply  of  lead  is  very  limited.  Much  is  lost  need- 
lessly by  the  prevailing  methods  o^'  mining,  milling,  and  smelting. 
About  one-third  of  the  lead  produced  in  the  United  States  is  used  in 
making  paint.  Lead  used  in  paint  can  be  used  but  once,  and  more 
abundant  things  will  have  to  be  substituted  for  it  increasingly  in  the 
future. 

Zinc  is  associated  in  many  places  with  lead,  and  for  years  was 
regarded  as  valueless  by  lead  miners.  The  first  zinc  plants  were 
erected  in  Illinois  in  the  1850's,  but  for  twenty  years  the  produc- 
tion was  small.  In  recent  years  it  has  increased  very  fast,  and 
the  output  of  the  last  decade  equaled  that  of  all  earlier  years.  Mis- 
souri leads,  by  a  large  margin,  in  its  production.  There  is  great  waste 
of  zinc  in  mining,  concentrating,  and  smelting.  About  two-thirds 
of  that  produced  in  this  country  is  used  for  galvanizing  iron.  Like 
lead,  it  is  used  also  for  making  paint.  Most  of  the  rest  is  used  (with 
copper)  for  making  brass,  and  for  sheet  zinc. 

In  191 1,  the  United  States  produced  406,000  tons  of  lead  and 
271,000  tons  of  zinc. 

Aluminum.  Aluminum  is  by  far  the  most  abundant  of  the 
metals.  It  is  a  constituent  of  many  rocks,  and  maket.  up  more  than 
8  per  cent  of  the  earth's  crust.  It  is  light,  strong,  malleable,  ductile, 
is  a  good  conductor  of  electricity,  takes  and  retains  a  high  polish, 
and  does  not  corrode  easily.  These  properties  fit  it  for  many  purposes,, 
but  the  diflSculty  and  expense  of  separating  it  from  its  combinations 
long  prevented  its  extensive  use.  It  is  extracted  on  a  commercial 
scale  only  from  bauxite,  a  relatively  scarce  mineral.  When  it  can  b* 
obtained  cheaply  from  clay,  of  which  it  forms  a  part,  its  use  wiU  be 
increased  enormously. 


CONSERVATION  OF  MINERAL  RESOURCES  183 

The  production  of  aluminum  in  the  United  States  increased  from 
83  pounds  in  1883  to  about  47,000,000  pounds  in  191 1.  It 
is  used  for  making  a  constantly  increasing  variety  of  things,  such 
as  cooking  utensils,  castings,  wall  "paper,"  ceiling  panels,  paints, 
varnishes,  and  wire.  Doubtless  in  the  future  it  will  replace  iron, 
copper,  and  some  of  the  other  metals  for  many  purposes. 

Salt 

Salt  is  indispensable  to  man,  and  fortunately  the  supply  is  prac- 
tically inexhaustible,  (i)  In  arid  regions  there  are  many  lakes 
with  no  outlets  into  which  streams  bring  minerals  (including  com- 
mon salt)  that  have  been  dissolved  during  the  passage  of  the  water 
through  or  over  the  rocks  (p.  211).  These  things  are  left  behind  as 
water  evaporates  from  the  lake,  which  becomes  more  and  more 
saline  as  the  process  continues.  When  the  waters  of  the  lake  become 
saturated,  further  evaporation  causes  the  minerals  to  begin  to  be 
precipitated  from  solution.  Great  Salt  Lake  is  estimated  to  contain 
some  400,000,000  tons  of  common  salt.  (2)  Extensive  salt  beds 
which  were  laid  down  in  ancient  lakes  or  arms  of  the  sea  are  found 
between  beds  of  other  rock  in  many  places.  Those  in  central  New 
York  may  have  an  area  underground  of  some  10,000  square  miles  (lar- 
ger than  Vermont),  and  single  beds  are  in  places  80  feet  thick.  Besides 
New  York,  Michigan  and  Kansas  are  leading  salt-producing  states. 
(3)  The  ocean  is  the  remaining  and  greatest  source  of  supply  (p.  144). 

The  need  of  salt  helped  to  hold  most  of  the  American  colonists  near  the  At- 
lantic coast  for  a  long  time.  Not  until  it  was  discovered  in  the  Holston  and  Kanaw- 
ha valleys  (Tenn.  and  W.  Va.),  in  central  New  York,  and  in  Kentucky,  did 
dependence  on  the  coast  for  salt  cease.  In  1778,  salt  brought  on  pack  animals 
over  the  Appalachian  Mountains  sold  in  southwestern  Pennsylvania  for  £6  ids. 
per  bushel.  The  same  amount  of  salt  now  is  worth  but  little  more  than  10  cents 
where  it  is  prepared,  and  not  more  than  50  cents  in  the  markets  in  most  parts  of 
the  United  States. 

Conservation  of  Mineral  Resources 

The  mineral  resources  noted  above  are  a  part  of  the  heritage 
of  the  earth.  The  people  of  to-day  have  a  right  to  use  such  of  them 
as  they  need,  in  as  great  quantities  as  necessary.  It  is  their  duty, 
however,  to  use  them  in  such  a  way  as  to  insure  the  minimum  of 
waste  and  the  maximum  of  efficiency.  This  is  demanded  alike 
by  the  interests  of  the  present  generation,  and  by  those  of  genera- 


i84        MATERIALS  OF  THE  LAND  —  THEIR  USES 

tions  to  come.  The  facts  given  show  that  many  reforms  are  needed. 
The  reckless  waste  of  some  of  these  resources  is  a  reflection  upon 
American  intelligence. 

Questions 

1 .  What  are  the  principal  ways  in  which  soil  is  being  formed  in  New  England? 
Florida?     Nevada? 

2.  Why  are  the  soils  of  the  lower  flood-plains  and  deltas  of  large  rivers  of  great 
fertility  in  most  cases?     Are  they  commonly  of  coarse  or  fine  texture?     Why? 

3.  State  conditions  which  explain  why  soil  wash  is,  in  some  cases,  much  faster 
on  one  of  two  equal  slopes  than  on  the  other. 

4.  Would  you  expect  wash  in  winter  from  bare  fields  to  be  greater  in  northern 
or  southern  United  States?     Why? 

5.  Would  it  be  desirable,  from  the  standpoint  of  agriculture,  entirely  to 
prevent  soil  erosion  if  it  were  possible?     Reasons? 

6.  Tile  underdraining  is  in  many  cases  effective  in  checking  soil  erosion.    Why? 

7.  Plowing  under  straw,  leaves,  etc.,  was  formerly  a  common  practice.  What 
value,  if  any,  would  this  have? 

8.  In  some  of  the  mountainous  areas  of  Italy,  .Austria,  and  other  countries, 
forests  are  maintained  in  strips  at  right  angles  to  the  slope  of  the  surface,  while 
the  land  between  is  tilled.     Why  is  this  advantageous? 

9.  Explain  in  detail  why  plowing  up  and  down  a  hill-side  is  unwise. 

10.  Other  things  being  equal,  would  you  expect  crops  to  suffer  more  from 
protracted  droughts  on  sandy  or  on  clayey  soils?     Why? 

11.  In  parts  of  China  it  is  customary  to  plant  alternate  rows  of  leguminous 
plants  (like  peas  and  beans)  and  grains.     How  does  this  benefit  the  soil? 

12.  Steel  cars  rapidly  are  replacing  wooden  ones,  and  re-enforced  concrete 
(i.e.,  cement  strengthened  by  steel)  is  being  used  for  many  new  oridges  in  place  of 
steel.  Are  these  changes  desirable  from  the  standpoint  of  tne  conservation  of 
natural  resources?     Reasons? 

13.  Why  are  gold  and  silver,  the  "precious  metals,"  mucn  fess  essential  to 
man  than  coal  and  iron? 


CHAPTER  XIV 

CHANGES  OF  THE   EARTH'S   SURFACE   DUE  TO   INTERNAL 

FORCES 

Slow  Crustal  Movements 

Except  for  occasional  earthquakes  and  landslides  the  crust  of  the 
earth  seems  to  be  firm  and  stable,  but  it  is  in  reality  subject  to  very 
slow  movements  which,  in  the  course  of  ages,  produce  great  changes. 
Such  movements  warp  both  land  and  sea-bottom.  It  is  probable 
that  more  of  the  earth 's  surface  has  been  sinking  or  rising  in  recent 
geological  times  than  has  been  standing  still. 

Movement  of  coastal  lands,  (i)  Old  buildings  and  docks, 
near  sea-level  when  built,  are  now  under  water  in  some  places  and 
well  above  the  sea  in  others.  Clearly,  this  means  a  recent  change,  at 
these  places,  in  the  relations  of  land  and  sea.  (2)  Beds  of  sediment 
containing  sea-shells,  deposited  beneath  the  sea  in  recent  times,  are 
found  above  the  water  in  north  Greenland,  on  the  Pacific  coast  of  the 
United  States,  in  the  West  Indies,  on  the  west  coast  of  South  America, 
and  in  other  places.  On  the  slopes  of  Mount  St.  Elias,  Alaska,  mod- 
ern sea-shells  have  been  found  attached  to  the  rocks  just  as  they 
once  grew,  but  several  thousand  feet  above  the  sea.  (3)  On  the 
other  hand,  there  are  drowned  forests  along  some  coasts.  Thus  north 
of  Liverpool,  England,  many  stumps  may  be  seen  at  low  tide  standing 
on  the  beach  (Fig.  88).  Since  trees  of  the  kind  represented  by  these 
Stumps  do  not  grow  in  salt-water,  it  is  clear  that  the  land  where  they 
grew  has  sunk  below  the  level  of  high  water.  On  the  coasts  of  New 
Jersey  and  North  Carolina,  too,  there  are  stumps  having  similar 
histories,  several  feet  below  sea-level.  These  and  many  other  facts 
prove  that  the  land  and  sea  change  their  relations  to  each  other,  and 
that  most  coast-lines  have  been  affected  by  such  changes  in  recent 
times. 

The  emergence  of  land  may  be  due  to  (i)  its  rise,  or  (2)  the  sink- 
ing of  the  sea-level.  Similarly,  the  submergence  of  land  may  be 
due  to  (i)  its  sinking,  or  (2)  the  rise  of  the  sea.     From  what  is  now 

1 8s 


i86 


CHANGES  OF  THE  EARTH'S  SURFACE 


known  it  is  certain  that  both  the  sea  and  the  land  rise  and  fall  from 
time  to  time. 

Causes  of  changes  in  sea-level.  Several  things  may  make  the 
sea-level  rise  or  fall,  (i)  The  sinking  of  a  part  of  the  ocean  bed  would 
lower  the  sea  surface,  while  the  elevation  of  a  part  of  the  sea  floor 
would  have  an  opposite  effect.     (2)  Sediment  washed  from  the  land 

into  the  sea  builds  up  the 
ocean  floor,  and  so  raises 
the  surface  of  the  sea. 
(3)  Lavas  poured  out 
from  volcanoes  beneath 
the  sea,  and  the  deposits 
of  corals  and  shell-bear- 
ing sea  life,  make  the 
sea-level  rise.  (4)  An 
increase  or  decrease  in 
the  total  amount  of  land- 
water  or  ice  would  lower 
or  raise  the  surface  of 
the  ocean.  Since  the 
oceans  are  all  connected 
one  with  another,  each 
of  the  above  changes 
would  affect  the  surface 
of  the  sea  everywhere,  and  by  the  same  amount.  Other  factors 
also  affect  the  surface  of  the  sea,  and  some  of  them  make  it  higher 
in  certain  places  than  in  others. 

Changes  of  level  in  the  interiors  of  continents.  Changes  of 
level  are  perhaps  as  common  in  the  interiors  of  continents  as  along 
coasts,  but  they  are  not  detected  so  easily,  since  there  is  no  level 
surface  like  the  sea  with  which  to  make  comparisons.  There  are 
raised  beaches  about  many  lakes,  as  about  the  Great  Lakes  and 
Great  Salt  Lake  (Fig.  89) ;  but  raised  beaches  about  a  lake  may  result 
from  the  lowering  of  the  lake,  either  by  the  cutting  down  of  its  outlet 
or  by  evaporation.  They  do  not,  therefore,  prove  a  rise  of  the  land. 
But  many  old  shore-lines  about  lakes  are  not  horizontal,  as  they  were 
when  formed.  Some  parts  of  the  old  shore-line  about  former  Lake 
Bonneville  (the  ancestor  of  Great  Salt  Lake)  are  300  feet  higher  than 
other  parts  of  the  same  line.  Similar  tilted  shore-lines  are  found  about 
many  lakes,  and  show  that  the  land  has  warped  since  the  shore-lines 


Fig.  88.  Stumps  laid  bare  on  the  beach 
at  low  tide;  Leasowe,  England.  (From  photo- 
graph by  Ward.) 


CHANGES  OF  LEVEL 


187 


were  formed.     Other  phenomena,  some  of  them  discussed  later,  also 
show  movement  of  large  interior  areas. 

Ancient  changes  of  level.  Layers  of  rock,  deposited  long  ago 
as  sediment  beneath  the  sea,  are  now  found  over  great  areas,  far 
above  sea-level.  Most  of  the  solid  rock  beneath  the  Mississippi 
Basin,  for  example,  was  laid  down  as  sediment  beneath  the  sea,  as 
shown  by  the  shells  of  the  sea  animals  which  it  contains.     In  the 


Fig.  89.     Shore  of  former  Lake  Bonneville,  Utah.     (From  photograph  by 
U.  S.  Geol.  Surv.) 

Appalachian  Mountains,  rocks  formed  in  the  same  way  are  found 
up  to  heights  of  several  thousand  feet;  in  the  Rocky  Mountains 
up  to  10,000  feet  and  more;  and  in  some  other  mountains  to  still 
greater  heights.  It  is  certain,  therefore,  that  changes  of  level  have 
been  great,  and  that  vast  areas  have  been  affected. 

It  is  also  certain  that  great  changes  in  the  areas  and  in  the  rela- 
tions of  land  and  sea  have  occurred  many  times  in  the  distant  past. 


Earthquakes 

Frequency  and  importance.  Tremblings  or  quakings  of  the 
earth's  surface  occur  frequently  in  many  countries.  Most  of  them 
are  not  felt,  and  can  be  detected  only  by  means  of  delicate  instru- 


i88 


CHANGES  OF  THE  EARTH'S  SURFACE 


merits  made  to  record  them.  For  many  years  an  average  of  several 
earth  tremors  a  day  have  been  recorded  in  Japan,  and  it  has  been  said 
that  some  part  of  the  earth's  surface  is  shaking  all  the  time.  The 
changes  made  in  the  surface  of  the  land  by  earthquakes  are  slight, 
and  they  are  important  chiefly  because  severe  earthquakes  may  cause 
great  loss  of  life  and  property. 

Distribution.  Most  earthquake  regions  lie  near  the  edges  of 
the  continental  platforms,  though  some  (in  Asia)  are  far  inland.     Most 

of  them  are  mountainous  areas, 
though  some  are  lowlands. 
Earthquakes  are  perhaps  most 
common  in  volcanic  regions, 
though  not  all  the  earthquakes 
of  such  regions  have  been 
caused  by  volcanoes.  Except 
along  the  west  coast  of  South 
America,  the  southern  conti- 
nents are  rather  free  from 
earthquakes,  or  at  least  few  are 
reported  from  them.  In  the 
northern  hemisphere,  earth- 
quakes are  most  common  about 
the  Mediterranean  Sea,  in 
southern  Asia,  in  the  islands 
east  and  southeast  of  that  con- 
tinent, and  along  the  western 
coasts  of  North  and  Central 
America.  Some  of  the  areas  most  affected  by  earthquakes  are 
settled  densely. 

Causes  of  earthquakes.  Earthquakes  are  caused  in  various  ways. 
During  movements  of  the  earth's  crust,  great  cracks  or  fissures 
sometimes  are  formed  in  the  surface  of  the  land  (Fig.  90).  The  walls 
of  fissures  may  be  displaced,  or  faulted.  Faulting  has  caused  many 
great  earthquakes,  the  slipping  of  one  great  body  of  rock  past  another 
producing  vibrations,  which  in  some  cases  have  spread  great  distances. 
An  Alaskan  earthquake  in  1899  was  caused  by  a  sudden  displacement 
of  more  than  40  feet,  and  the  San  Francisco  disaster  in  1906  resulted 
from  a  horizontal  movement  of  5  to  20  or  more  feet,  along  a  line  many 
miles  in  length.  Earthquakes  accompany  violent  volcanic  eruptions, 
and  in  these  cases  the  explosions  which  accompany  the  eruptions 


■ii-  ta^ 

^JKmjk 

^^HHP^^'^  ^^4^; 

m^m 

BB^MSa'yiBMP^P  % 

K^^^HHiESf 

^^^^^pE^^^  ■ 

'>'<^ll^^^^^^^^^l 

^^Sf>^Kvt^_                             ^^^V 

r|V|^^  ■■iiii 

Fig.  90.     Fissure  in  floor  of  Kilauea, 
Hawaii. 


DESTRUCTION  BY  EARTHQUAKES 


i8o 


doubtless  cause  the  quaking.  Great  landslides  and  avalanche"* 
rnay  cause  slight  earthquakes.  Slight  shocks  may  be  caused  in  stili 
other  ways. 

It  is  probable  that  most  earthquakes  are  incidents  of  the  wide- 
spread movements  to  which  the  crust  of  the  earth  is  subject,  move- 
ments which  are  due  chiefly  to  the  continued  fitting  of  the  outside  of 
the  earth  to  a  shrinking  interior.  In  general,  these  movements  are 
too  slow  to  produce  vibrations  which  we  can  feel ;  but  they  are  sufficient, 
in  rare  cases,  to  produce  great  earthquakes. 

Destruction  of  life  and  property.  Except  along  the  plane  of 
slipping,  the  actual  movement  of  the  land  surface  during  an  earth- 


Fig.  91.    The  new  library  building  at  Stanford  University,  after  the  earth- 
quake of  April,  1906.     (Moran.) 


quake  is  very  slight,  in  most  cases  only  a  small  fraction  of  an  inch. 
It  is  the  suddenness  of  the  shock  which  overthrows  and  destroys 
buildings  and  other  objects.  That  a  sudden  but  very  slight  movement 
of  the  ground  may  do  this  is  clear  from  the  fact  that  a  quick,  sharp 
tap  on  the  side  of  a  table  may  overthrow  all  loose  objects  upon  it, 
even  though  the  movement  of  the  table  Itself  is  very  slight. 

Some  earthquakes  in  thickly  settled  regions  have  caused  an  appal- 
ling loss  of  life  and  property.  The  most  disastrous  earthquake  in 
North  America  occurred  in  and  about  San  Francisco  in  April,  1906. 
A  large  part  of  the  city  was  burned  by  the  fire  which  followed  the 
shock.  More  than  700  lives  were  lost,  and  between  100,000  and 
200,000  people  were  made  homeless.     Some  25,000  buildings  (Fig.  91) 


loo     CHANGES  OF  THE  EARTH'S  SURFACE 

were  destroyed  in  the  earthquake  and  fire,  having  an  estimated  val'.ie 
ot  more  than  $100,000,000.     In  1905  a  great  earthquake  in  India 


Fig.  92.    Taal  Volcano,  Philippine  Islands,  in  eruption.     (Gilchrist.) 

destroyed  nearly  19,000  lives  and  more  than  1 12,000  buildings.     About 
100,000  people  were  killed  in  the  earthquakes  in  southern  Italy  in  1908. 


TYPES  OF  VOLCANOES 


IQI 


In  some  countries  where  earthquakes  are  frequent,  like  Japan, 
much  attention  has  been  given  to  making  buildings  in  such  a  way  as 
to  withstand  the  shocks.  The  greater  frequency  of  earthquakes 
m  Nicaragua  was  one  reason  for  selecting  the  Panama  route  for  the 
Isthmian  Canal. 

When  an  earthquake  disturbs  the  sea-bottom,  waves  are  set  in 
motion.  These  waves  rush  upon  neighboring  coasts,  and  in  some  cases 
(e.  g.,  in  Sicily  in  1908)  they  have  done  great  damage.  Millions  of 
marine  animals  and  plants  were  killed  during  the  Alaskan  earthquake 
of  1899. 

VULCANISM 

Volcanoes 

A  volcano  is  a  vent  in  the  earth's  crust  out  of  which  hot  rock 
comes  (Fig.  92).  The  hot  rock  may  flow  out  in  liquid  form  (called 
lava),  or  it  may  be  thrown  out  violently  in  solid  pieces.  It  is  gen- 
erally built  up  into  a 
cone  (Fig.  93),  which 
may  become  a  mound,  a 
high  hill,  or  even  a  high 
mountain.  Quantities 
of  gases  and  vapors  are 
discharged  along  with 
the  hot  rock.  There  is 
a  hollow,  called  the 
crater,  in  the  top  of 
most  volcanic  cones. 
Craters  vary  greatly  in 
size,  some  of  the  larger 
ones  being  two  or  three 
miles  across.  While 
the  volcano  is  active, 
an  opening  leads  down 
from  the  crater  to  the  source  of  the  lava,  at  an  unknown  depth. 

Common  phenomena  of  an  eruption.  In  the  explosive  type 
of  eruption,  rumblings  and  earthquake  shocks,  due  to  explosions 
within  the  throat  of  the  volcano,  may  occur  for  weeks  or  montht 
before  a  violent  outbreak.  During  a  violent  outbreak,  dust,  cinders, 
and  larger  pieces  of  rock  are  shot  forth  and  fall  on  the  sides  of  the  cone 
The  clouds  of  condensed  steam  and  dust  rising  from  the  crater  darken 


Fig.  93- 
(Marshall.) 


Cone  of  Ngauruhoe,  New  Zealand. 


19^ 


CHANGES  OF  THE  EARTH'S  SURFACE 


the  sky,  and  torrents  of  rain,  falling  on  the  fine  dust,  may  form  rivers 
of  hot  mud.  Liquid  lava  may  or  may  not  accompany  the  discharge  ox 
solid  material.  In  the  quiet  type  of  eruption,  the  lava  rises  in  the 
crater  and  overflows  its  rim  or,  more  often,  breaks  out  through  cracks 
in  the  side  of  the  cone.  There  is  little  or  no  burning  in  a  volcano, 
tor  there  is  little  or  nothing  to  burn.  There  is,  therefore,  no  smoke. 
What  appears  as  smoke  is  mostly  cloud,  blackened  by  volcanic  dust. 
The  products  of  volcanoes.  Lava  is  a  term  applied  both  to 
the  liquid  rock  which  issues  from  a  volcano,  and  to  the  solid  rock 


Fig.  94.     Recent  flow  of  lava  from  Kilauea,  Hawaii.     (U.  S.  Forest  Service.) 


which  results  from  its  cooling  (Fig.  94).  Most  of  the  solid  materials 
blown  out  of  a  volcano  are  pieces  of  lava  which  became  solid  before 
they  were  shot  out,  or  during  their  flight  in  the  air.  They  include 
masses  of  rock  tons  in  weight,  and  smaller  pieces  of  all  sizes  down  to 
particles  of  dust  (commonly  called  volcanic  ash).  The  dust  in  many 
cases  is  shot  high  into  the  air,  and,  being  light,  is  scattered  broadcast 
by  the  winds,  some  of  it  coming  to  rest  thousands  of  miles  away. 
The  liquid  lava  and  the  larger  solid  pieces,  on  the  other  hand,  stay 
near  the  vent. 

The  gases  and  vapors  which  issue  from  volcanoes  are  of  many 
kinds.  Some  are  poisonous,  and  some  are  so  hot  as  to  be  destructive 
to  life,  as  in  the  case  of  Mont  Pelee,  in  1902  (p.  197). 


TOPOGRAPHIC  EFFECTS  OF  VOLCANOES 


10^ 


Soils  made  by  the  decay  of  volcanic  materials  may  be  very 
fertile  if  well  watered.  The  volcanic  soils  of  the  Spice  Islands 
(Moluccas),  Java,  and  other  islands  of  the  East  Indies,  support  a 
luxuriant  vegetation. 

Number.  The  number  of  active  volcanoes  is  not  known,  but 
is  estimated  at  300  to  400.  Something  like  two-thirds  of  them  are 
on  islands,  and  the  rest  on  the  continents. 

Distribution.  The  distribution  of  active  volcanoes  is  shown  in 
Fig.  95.     Many  are  in  belts,  within  which  some  are  in  lines.     The 


fl  KTWE  vOi£AJtOC« 


+  KOEMTL1  EXTINCT  VOCCANOU 


Fig.  95.     Map  showing  the  distribution  of  volcanoes.     (Russell.) 

most  marked  belt  nearly  encircles  the  Pacific  Ocean.  The  volcanoes 
of  the  West  Indies  and  of  Java  and  Sumatra  sometimes  are  considered 
as  forming  branches  of  the  main  belt.  Outside  this  belt,  there  are 
a  number  of  volcanoes  in  and  about  the  Mediterranean  Sea,  and 
there  are  others  which  are  not  connected  with  any  well-marked 
system. 

Most  volcanoes  are  in  the  sea  or  near  it.  Many  are  in  moun- 
tain regions,  though  they  do  not  occur  in  all  mountains.  Many  of 
the  active  volcanoes  are  near  the  line  where  the  continental  plateaus 
descend  to  the  ocean  basins.  Many  volcanoes  are  in  lands  which 
have  been  raised  or  lowered  recently. 

Topographic  effects  of  volcanoes.  Some  volcanic  cones  are 
mountains  of  great  size,  like  Mt.  Rainier  (Tacoma)  in  Washington, 


194 


CHANGES  OF  THE  EARTH'S  SURFACE 


Mt.  Hood  in  Oregon  (Fig.  96),  Mt.  Shasta  in  California,  and  Orizaba 

in  Mexico.     All  those  named  are  so  high  that  glaciers  are  found 

on  their  slopes.  Vol- 
canic cones  are  far 
more  numerous  than 
volcanoes,  for  the 
cones  of  many  ex- 
tinct volcanoes  still 
remain. 

Many  small  islands 
and  some  large  ones 
are  due  chiefl)^  or 
wholly  to  the  build- 
ing of  volcanic  cones 
on  the  ocean-bottom. 
The  Aleutian  Islands 

and  the  Hawaiian  Islands  were  formed  in  this  way.     Iceland,  too, 

is  largely  volcanic. 

Destruction  of  volcanic  cones.    Volcanic  mountains,  like  all 

other  elevations  on  the  land,  are  subject  to  change  and  destruction. 


Fig.  96.     Mt.  Hood,  a  snow-capped  mountain. 


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wMh            ''^C^^^H 

n 

^H     ' '      ''^jLi'    "jC                                 i^^^^^H 

K 

^^^^Hh^^^^^^Wk^  ^H^>                           /^^^^^^^l 

Fig.  97.     Portion  of  Crater  Lake,  Oregon.     (Copyright  by  Riser  Photo  Co.) 


DESTRUCTION  OF  VOLCANIC   CONL 


-■i? 


They  may  be  destroyed  partially  by  violent  explosions. 

top  of  a  volcanic  mountain  may  sink,  leaving  a  great  K, 

caldera.     Crater  Lake,  Oregon  (Fig.  97),  the  deepest  lake  \ 

America,  is  in  a  caldera  five  or  six  miles  in  diameter,  and  4,c   -j  teet 

deep.     The  lake  is  sur-  ^        _  ^ 

rounded  by  steep  walls 

900  to  2,200  feet  high. 

Since   the    sinking   of 

the  top,  a  small  cone, 

now  an  island  in  the 

lake,  has  been  built. 

Volcanic  cones  are 
destroyed  also  by  the 
slow  processes  of  weath-  Y\g.  98. 

ering    and    erosion      California, 
(p.  306).     Wind  and 

rain  attack  them  as  soon  as  they  are  formed,  but  the  results  are  not 
striking  until  the  volcano  is  extinct  and  the  cone  stops  growing.  The 
many  cones  of  extinct  volcanoes  in  western  United  States  are  in 
various  stages  of  destruction.     Some  in  Arizona,  California  (Fig.  98), 


Typical  cinder  cone,  Clayton  Valley, 


Fig.  99.     Mt.  Shasta,  a  t5T3ical  volcanic  cone  furrowed  by  erosion,  but  retaiia- 
ing  its  general  form.     (U.  S.  Geol.  Surv.) 


Idaho,  and  Oregon  were  formed  so  recently  that  they  have  been 
eroded  but  little.  Fig.  99  shows  a  high  mountain  built  by  a 
former  volcano.  It  still  retains  its  conical  form,  but  its  steep  upper 
slopes  are  cut  by  ravines  and  valleys,  several  of  which  contain 
glaciers. 


196 


CHANGES  OF  THE  EARTH'S  SURFACE 


Destructiveness.  Like  earthquakes,  some  volcanoes  have  de- 
stroyed great  numbers  of  Hves  and  much  property.  During  an  erup- 
tion of  Vesuvius  in  79  A.  D.,  Pompeii,  a  city  of  about  20,000  people. 


Fig.  100.     The  ruins  of  Pompeii.     (Dosefif.) 

was  buried  by  cinders  and  ashes  (Fig.  100),  and  Herculaneum  was 
overwhelmed  by  streams  of  hot  mud.  Some  of  the  later  eruptions 
of  this  volcano  also  have  been  very  destructive.     That  of   1631 


Lang  I. 


Fig.  lOI  Fig.  102. 

Fig.  loi.     Krakatoa  Island  and  surroundings  before  the  eruption  of  1883. 

Fig.  102.  Kraliatoa  Island  and  surroundings  after  the  eruption  of  1883. 
The  numbers  indicate  the  depth  of  the  water  in  fathoms  (a  fathom  =  6  feet)  in 
both  figures. 

destroyed  some  18,000  lives.  One  of  the  most  violent  and  destructive 
volcanic  eruptions  known  was  that  of  1883  in  Krakatoa,  an  island 
between  Sumatra  and    Java.     About  two-thirds  of  the  island  was 


LOSSES  DUE  TO  VOLCANOES 


197 


blown  away,  and  the  sea  is  now  nearly  i  ,000  feet  deep  where  the  center 
of  the  mountain  formerly  was  (Figs.  loi  and  102),  Sea  waves  spread 
to  Cape  Horn,  and  possibly  to  the  English  Channel.  On  the  shores 
of  neighboring  islands  the  water  rose  50  feet.  More  than  36,000 
persons  perished,  mostly  by  drowning,  and  295  villages  were  destroyed, 
wholly  or  partially. 

The  volcano  of  Pelee  is  on  the  island  of  Martinique,  at  the  eastern 
edge  of  the  Caribbean  Sea.  Its  cone  descends  by  steep  slopes  to  the 
sea  on  all  sides  but  the 
south,  where  there  is  a 
plain  on  which  the  city  of 
St.  Pierre  formerly  stood. 
After  slumbering  for  more 
than  fifty  years,  the  vol- 
cano became  active  in  the 
spring  of  1902.  On  May 
8th  a  heavy  black  cloud, 
probably  composed  of 
steam,  sulphurous  vapors, 
and  dust,  which  had  an 
estimated  temperature  of 
1,400°  to  1,500°  F.,  swept 
down  through  a  gash  in 
the  crater's  rim,  and  out 
over  the  plain  to  the  south- 
west. In  two  minutes  it  struck  the  city  of  St.  Pierre,  five  miles 
distant,  which  was  demolished  at  once  (Fig.  103).  Buildings  were 
thrown  down,  statues  hurled  to  the  ground,  and  trees  torn  up. 
Explosions  were  heard  in  the  city  as  the  cloud  reached  it,  and  flames 
burst  out,  started  either  by  the  heat  of  the  gases,  or  by  the  red-hot 
particles  of  rock  which  the  gases  carried.  A  few  minutes  later  a 
deluge  of  rain,  mud,  and  stones  fell,  continuing  the  destruction.  Only 
two  people  out  of  30,000  survived  the  disaster. 

Igneous  Phenomena  Not  Strictly  Volcanic 
Fissure  eruptions.  Lava  sometimes  rises  to  the  surface  through 
great  cracks  instead  of  through  the  rather  small  vents  of  vol- 
canoes. From  such  cracks  floods  of  lava  may  spread  over  the 
land  for  hundreds  of  miles.  Many  such  lava  floods  once  occurred 
in  Oregon,  Washington,  and  Idaho,  where  the  former  hills  and 


Fig.  103.    The  ruins  of  St.  Pierre,  Mar- 
tinique.    (Hovey.) 


iqS 


CHANGES  OF  THE  EARTH  ^S  SURFACE 


Fig.  104.    Lava  flows  of  the  North- 


west. 


valleys  were  buried,  and  a  vast  plateau   200,000  square  miles  or 
more  in  extent  was  built  up  (Fig.  104).     In  this  lava  plateau,  the 

Snake  River  has  cut  a  great 
canyon  4,000  feet  deep  in  some 
places,  and  15  miles  wide.  The 
walls  of  the  canyon  show  that 
in  some  cases  successive  beds 
of  lava  are  separated  by 
layers  of  soil  in  which  the 
roots  and  trunks  of  trees  are 
preserved. 

An  older  and  larger  lava 
plateau,  more  dissected  by 
erosion,  occurs  in  central  and 
southern  India.  Still  others, 
now  made  rough  by  erosion, 
are  found  in  northern  Ireland 
and  western  Scotland.  Some  of  the  islands  off  Scotland  are  rem- 
nants of  an  old  lava  plateau. 

Intrusions  of  lava.    Most  of  the  lava  forced  upward  from  great 
depths  probably  fails  to  reach  the  surface,  and  hardens  underground. 

Such  rocks  may  be  exposed  at 
the  surface  through  the  wear- 
ing away  of  the  rocks  which 
overlay  them.  Great  masses  of 
intruded  lava  may  bulge  up  the 
overlying  strata,  making  domes 
(Fig.  105),  some  of  which  reach 
the  size  of  mountains.  The 
Henry  Mountains  of  Utah  are 
examples.  In  places,  lava  has 
been  forced  in  between  beds  of 
rock,  and  into  cracks  in  them 
(Fig.  106). 

Intrusions  of  lava  may  give 
rise  to  topographic  features  of 
importance  after  erosion  has 
affected  the  regions  where  they 
occur,  for  the  hardened  lava  is 
in  many  cases  harder  than  its 


Fig.  105.     Diagram  of  a  laccolith. 


Fig.  106.  Diagram  showing  lava 
which  has  been  forced  in  between  beds  of 
rock  (k)rming  sills),  and  into  cracks 
(forming  dikes).  What  changes  have  oc- 
curred since  the  dike-rock  was  intruded? 


CAUSES  OF  VULCANISM 


199 


surroundings.  Many  dikes  form  ridges.  Intruded  sheets  of  lava,  if 
they  have  been  tilted  from  a  horizontal  position,  may  also  form  ridges, 
and  these  ridges  may  be  so  high  as  to  be  called  mountains.  The 
Palisade  Ridge  of  the  Hudson  (Fig.  107),  and  most  of  the  mountains 


■'^^-S^^J^'" 


Fig.  107.     The  face  of  the  Palisade  Ridge,  west  of  the  lower  Hudson  River. 


of  the  Connecticut  Valley,  are  examples.  The  steep  ridges  so  impor- 
tant in  the  battle  of  Gettysburg  are  smaller  examples  of  the  same 
sort. 

Causes  of  Vulcanism 

The  causes  of  vulcanism  are  not  well  known.  How  the  liquid 
rock  is  formed,  the  depth  of  its  source,  and  how  it  makes  its  way  to- 
ward the  surface,  are  unsolved  questions.  The  old  notion  that 
volcanic  vents  are  connected  with  a  liquid  interior  has  been 
abandoned. 

It  seems  probable  (i)  that  lava  is  being  formed  all  the  time, 
in  spots,  in  the  deep  interior,  and  (2)  that  it  is  all  the  time  finding 
its  way  toward  the  surface,  but  faster  and  in  greater  amounts  at 
some  times  than  at  others.  The  places  where  the  crust  is  weakest, 
that  is,  where  there  is  movement,  are  the  places  most  likely  to  afford 
the  lava  a  place  of  escape. 


200 


CHANGES  OF  THE  EARTH'S  SURFACE 


Questions 

I.  At  the  west  end  of  the  island  of  Crete,  in  the  Mediterranean  Sea,  old  docks, 
near  sea-level  when  built,  are  found  many  feet  above  the  water.  At  the  east  end 
of  the  island,  ancient  buildmgs  are  under  water.     Was  the  change  in  the  relation 

of  land  and  sea  thus  recorded  due  to 
movement  of  the  sea  surface,  or  of  the 
land?  Why  could  it  not  have  been  due  to 
the  other? 

2.  How  would  the  coast-line  of  North 
America  be  changed  if  the  bottom  of  the 
Indian  Ocean  were  to  sink  enough  to  lower 
the  surface  of  that  sea  200  feet? 

3.  Other  things  being  equal,  which 
are  more  enduring,  volcanic  cones  built  of 
lava  or  of  cinders?     Why? 

4.  Will   soil  form  quickly  or  slowly 
on  the  recent  (190?)  volcanic  deposits  of  Martinique  and  St.  Vincent?     Why? 

5.  (i)  What  was  the  origin  of  the  mountain  in  the  right  hand  foreground  of 
Fig.  108?  The  evidence?  (2)  Has  much  or  little  time  elapsed  since  its  formation' 
How  told?     (3)  What  is  the  probable  history  of  the  curving  ridge  at  the  left? 


d/yJA  ^"^^ 


Fig.  108. 


CHAPTER  XV 
MODIFICATION   OF  LAND   SURFACES   BY   EXTERNAL  AGENTS 

The  surface  of  the  land  is  being  changed  all  the  time  by  various 
agents,  especially  by  wind,  by  water  in  the  ground,  by  running  water, 
by  ice,  and  in  minor  ways  by  different  forms  of  life. 

The  Work  of  the  Wind 

Winds  change  land  surfaces  by  taking  dust  and  sand  from  certain 
places  and  depositing  them  in  others.  Wind-driven  dust  and  sand 
may  wear  exposed  surfaces  of  rock. 

Transportation.  Desert  winds  often  sweep  up  "clouds"  of 
dust  which  may  be  seen  for  miles,  and  a  single  storm  may  move 
millions  of  tons  of  dust  and  sand.  The  dreaded  simoon  of  the  Sahara 
has  been  known  to  destroy  entire  caravans,  death  resulting  from 
suffocation  in  the  dust-laden  air.  While  transportation  by  the  wind 
is  most  important  in  arid  regions,  it  is  not  confined  to  them.  Dry 
sand  and  dust  are  blown  about  wherever  they  are  exposed  to  the 
wind. 

Particles  of  dust  are  much  heavier  than  air,  and  gravity  tends 
to  bring  them  down.  Yet  they  may  remain  in  the  air  for  a  long 
time  (i)  because  they  are  so  small  that  they  do  not  fall  readily, 
and  (2)  because  there  are  many  upward  currents  in  the  air  which 
carry  them  up  in  spite  of  gravity.  As  a  matter  of  fact,  the  dust  of  the 
air  always  is  settling,  and  the  supply  is  being  renewed  all  the  time. 
Dust  in  the  air  may  be  carried  great  distances.  A  severe  storm  in 
March,  1901,  carried  dust  northward  from  the  Sahara  as  far  as 
Denmark.  In  1883,  volcanic  dust  from  Krakatoa  (p.  196)  was 
carried  around  the  earth  by  the  upper  winds  in  about  two  weeks, 
its  progress  being  shown  by  the  brilliant  sunsets  to  which  it 
gave  rise. 

Abrasion.  Sand  blown  against  a  rock  has  the  effect  of  a  sand- 
blast, and  wears  the  rock  away.     Abundant  Wind-blown  sand,  driven 

20I 


202 


MODIFICATION  OF  LAND   SURFACES 


Fig.  log.  Rockscarvedby  the  wind. 
(Bastin.)  What  inferences  may  be  made 
concerning  the  character  of  the  rocks? 


against  projecting  rocks,  may  carve  them  into  fantastic  forms  (Fig. 
109).     Tliis  process  is  of  much  importance  in  dry  regions  where  the 

land  is  rough.  In  deserts  and 
along  sea  coasts,  telegraph  poles 
have  been  cut  off  near  the 
ground  by  A\'ind-blown  sand. 
In  some  such  places,  stones  are 
piled  about  the  bases  of  the 
poles  to  protect  them  (Fig.  no). 
Wind  deposits.  Wind  de- 
posits of  sand  and  loess  have 
been  described  (p.  165).  Sand 
usually  is  blown  along  within  a 
few  feet  of  the  ground,  and  is 
therefore  likely  to  lodge  about 
any  obstacle  which  blocks  its 
way.  Mounds,  hills,  and  ridges 
of  wind-deposited  sand  are 
dunes,  which  range  in  height 
from  a  few  feet  to  more  than  400  feet.  Small  dunes  are  much  more 
common  than  large  ones.     Dunes  are  found  mostly  near  the  sources 

of  abundant  dry  sand.  They  are  common 
along  much  of  the  Atlantic  coast  of  the 
United  States,  where  sand  is  washed  up  on 
the  beach  by  waves.  After  drying,  it  is 
blown  about  by  the  wind.  Winds  from  the 
west  blow  this  sand  into  the  sea,  but  those 
from  other  directions,  especially  from  the 
east,  drift  it  up  on  the  land.  Dunes  abound 
over  thousands  of  square  miles  in  the  drier 
parts  of  the  Great  Plains,  as  in  western 
^■L  Nebraska  and  western  Kansas.     They  are 

^^^'  -* —  largest  and  most  numerous  in  still  drier  re- 
gions, as  the  Sahara.  In  some  places,  dunes 
are  the  most  striking  feature  of  the  landscape. 
Sand  is  blown  from  the  windward  side 
of  a  dune  and  dropped  on  the  leeward  side, 
much  of  the  time.  This  continued  shifting 
of  sand  to  the  leeward  side  results  in  a  slow  migration  of  the  dune. 
Farm  lands  have  been  covered  in  this  way,  and  forests  have  been 


Fig.  no.  Telegraph 
pole  in  southern  Cahfor- 
nia,  deeply  cut  by  wind- 
driven  sand.  (Menden- 
hall,  U.  S.  Geol.  Surv.) 


DAMAGE  DONE  BY  SHIFTING  SAND 


203 


Fig.  III.     Dunes  advancing  on  a  forest.     Little  Point  Sable.  Michigan. 


Fig.  112.     Biggs,  Ore.,  in  1899.     The  site  of  the  former  village  was  covered 
by  dunes,  and  the  last  house  was  being  torn  down.     (Gilbert,  U.  S.  Geol.  Surv.) 


204 


MODIFICATION  OF  LAND   SURFACES 


buried  (Fig.  iii).  In  some  places  sand  buries  buildings  (Fig.  112),  and 
causes  much  trouble  along  railways.  The  migration  of  dunes  along 
some  coasts  is  so  disastrous  that  steps  are  taken  to  stop  it.  If  a  dune 
is  covered  with  vegetation,  its  position  is  not  likely  to  change  so  long 
as  the  plants  remain,  for  they  hold  the  sand.  Trees,  shrubs,  and 
grasses  which  will  grow  in  sand  sometimes  are  planted  on  dunes  to 
prevent  further  drifting  (Fig.  113).  This  has  been  done  at  various 
points  on  the  western  coast  of  Europe,  and  to  some  extent  in  our 


Fig.  113.     Sand  dune  reclamation, 
from  photograph  by  Forest  Service.) 


Manistee  County,  Michigan.     (Sketch 


own  country,  as  at  San  Francisco,  where  the  westerly  winds  drift  sand 
in  from  the  shore.  The  amount  of  wind-blown  sand  not  heaped  up  in 
dunes  is  probably  far  greater  than  that  in  dunes. 

Summary.  The  more  important  phases  of  the  work  of  the 
atmosphere  may  be  summarized  here,  (i)  Of  most  importance  is 
its  work  as  an  agent  of  weathering  (pp.  161-164).  Through  its 
effect  on  changes  in  temperature  it  helps  to  break  rocks,  and  by 
the  chemical  action  of  its  oxygen,  carbon  dioxide,  and  water  vapor, 
it  causes  rocks  to  decay.  Weathering  prepares  materials  for  removal 
by  various  agents  of  transportation.  (2)  The  wind  transports  and 
deposits  large  amounts  of  fine  material.  Although  most  extensive 
in  arid  regions,  this  work  has  afifected  all  land  surfaces.  Since  the 
wind  deposits  much  dust  and  sand  in  the  sea,  the  general  effect  is 
to  lower  the  lands  and  build  up  the  ocean-bottoms.  (3)  Rocks  are 
worn  by  wind-driven  sand.  This  is  most  important  in  deserts,  where 
the  atmosphere  is,  in  many  places,  the  chief  agent  in  wearing  down 
the  land.     (4)  By  controlling  the  conditions  of  evaporation  and  pre- 


WATER  UNDERGROUND  205 

cipitation,  the  atmosphere  makes  possible  the  work  of  streams  and 
of  glaciers,  and  the  existence  of  land  life. 

QUESTIONS 

1.  Why  are  there  many  dunes  on  the  eastern  side  of  Lake  Michigan,  and  but 
few  on  the  western? 

2.  In  most  dune  areas  there  are  many  hollows  among  the  sand  hills.  In 
what  ways  are  such  hollows  formed? 

3.  Why  are  dunes  formed  along  some  river  valleys  and  not  along  others? 

4.  What  changes  in  natural  conditions  may  stop  dune-building  in  a  given 
region? 

Ground-Water 
general  considerations 

The  fate  of  rain-water.  The  average  annual  rainfall  of  the 
United  States  is  about  thirty  inches.  This  means  that  a  total  of 
about  1,500  cubic  miles  of  water  (enough  to  cover  New  England  to 
a  depth  of  about  1,000  feet)  fall  as  rain  or  snow  in  this  country  each 
year.  It  is  thought  that  about  half  of  this  water  evaporates,  that 
about  one-third  of  it  runs  off  over  the  surface,  and  that  the  remain- 
ing one-sixth  is  taken  up  by  plants  or  sinks  into  the  ground. 

The  ground-water  surface.  It  is  possible  almost  anywhere 
to  dig  wells  deep  enough  so  that  they  will  contain  water  all  the  time. 
This  means  that  the  surrounding  rocks  are  full  of  water  below  the 
level  of  the  water  in  the  wells.  The  surface  below  which  the  ground 
is  full  of  water  in  any  given  region  is  the  water  surface  or  water  table 
for  that  region.  In  swamps  and  marshes  the  water  table  is  at  or 
near  the  surface  of  the  ground,  while  in  arid  regions  it  may  be  hundreds 
of  feet  below.  In  humid  regions  it  is  seldom  more  than  50  or  60  feet 
below  the  surface.  The  position  of  the  water  table  also  varies  from 
time  to  time.  It  is  higher  after  heavy  rains,  and  lower  during  and 
after  long  droughts. 

Amount  of  water  underground.  The  pores  and  openings  in 
the  rocks  below  the  water  surface  are  full  of  water.  Some  porous 
rocks  contain  one-third  or  more  of  their  volume  of  water;  very  com- 
pact rocks  contain  but  little.  In  general,  rocks  near  the  surface  have 
more  and  larger  pores  and  cracks  than  those  at  greater  depths.  Pores 
and  cracks  become  very  small  at  the  depth  of  a  few  thousand  feet, 
and  probably  none  exist  below  a  depth  of  five  or  six  miles.  If  this 
is  true,  water  does  not  descend  to  greater  depths.     There  is  water 


2o6 


MODIFICATION  OF  LAND   SURFACES 


enough  underground  so  that,  if  it  were  brought  to  the  surface,  it 
would  form  a  layer  probably  500  to  1,000  feet  deep. 

Circulation  of  ground-water.  Ground-water  is  moving  all  the 
time.  This  is  shown,  for  example,  by  the  constant  flow  of  springs, 
and  by  the  fact  that  after  a  well  is  pumped  "dry,"  it  soon  fills  again 
to  the  former  level,  because  water  seeps  in  from  the  surrounding  rocks. 
Ground-water  moves  because  the  water  table  is  not  level  every- 
where, and  the  water  moves  from  places  where  its  surface  is  higher 
to  places  where  it  is  lower.     The  water  table  is  kept  uneven,  partly 


Fig.  114.     Diagram  showing  the  relation  of  the  level  of  ground-water  (the 
broken  line)  to  the  surface  of  the  ground  and  to  a  lake  and  river. 


because  of  unequal  rainfall,  and  partly  because  of  the  uneven  surface 
of  the  land.  Other  things  being  equal,  the  water  table  is  higher  beneath 
high  land,  and  lower  beneath  low  land  (Fig.  114).  The  water  surface 
below  the  high  land  tends  to  sink  until  it  is  as  low  as  that  beneath 
the  low  land;  but  in  moist  climates  it  rains  so  often  that  the  water 
surface  under  the  hills  almost  never  sinks  to  the  level  of  the  water  in 
the  surrounding  low  lands,  before  it  is  raised  again  by  rains. 

Water  which  sinks  to  great  depths  commonly  follows  an  irregular 
course.  At  first  its  movement  is  chiefly  downward,  and  is  rather 
rapid  because  of  the  many  large  cracks  and  pores  in  the  rocks  near  the 
surface.  Farther  down,  its  movement  is  largely  sideways  (Why?). 
It  may  flow  slowly  for  many  miles  along  a  crooked  course,  through 
small  openings,  before  it  reaches  a  passageway  leading  to  the  surface. 
Through  such  an  opening  it  may  issue  with  great  force  as  a  spring  or 
flowing  well.  Fig.  115  suggests  the  intricate  circulation  of  the  water 
which  issues  in  a  deep-seated  spring.  Some  water  flows  underground 
to  the  sea  or  to  lakes,  and  issues  as  springs  beneath  them.     Much 


MOVEMENTS  OF  GROUND-WATER 


207 


ground-water,  too,  seeps  out  in  such  small  amounts  that  it  does  not 
appear  to  flow,  and  does  not  make  a  spring. 

Much  ground-water  is  taken  up  by  roots,  passes  up  through  the 
plants,  and  comes  out  through  their  leaves  (is  transpired)  into  the  air. 
The  amount  of  water  returned  to  the  air  daily  by  forests  through  their 
foliage  varies  under  different  conditions  from  1,000  to  20,000  or  more 
pounds  per  acre,  during  the  growing  season.  About  5,000  pounds 
of  water  are  transpired  by  the  foliage  of  corn-plants  in  the  production 
of  a  bushel  of  corn.  Again, 
water  is  evaporating  from  the 
ground  most  of  the  time,  even 
in  regions  where  the  soil  appears 
to  be  very  dry. 

The  rate  at  which  ground-water 
moves  depends  chiefly  on  (i)  the 
porosity  of  the  rock  or  soil,  anu  (2) 
the  pressure  of  the  water.  The  rate 
at  which  water  seeps  through  soils 
from  irrigating  ditches  in  the  West  is 
in  most  cases  from  one  to  eight  feet 
per  day;  but  in  very  porous  soils  it 
is  sometimes  50  feet  per  day.  In 
widespread  beds  of  sandstone  which 

underlie  southern  Wisconsin  and  northern  Illinois,  the  rate  of  movement  of  ground- 
water is  about  half  a  mile  a  year.  At  this  rate,  rain-water  which  enters  these  beds 
100  miles  from  Chicago  would  reach  that  city  in  about  200  years. 

Knowledge  of  the  circulation  of  the  upper  part  of  the  ground- 
water is  important  to  every  family  using  well-water  for  household 
purposes.  Polluted  well-water  is  very  common  on  farms  which 
might  have  pure  and  wholesome  water.  Great  numbers  of  wells 
are  so  situated  that  ground-water  moves  toward  them  from  cess- 
pools and  stables.  Largely  as  a  result  of  this,  typhoid  fever  is  more 
common  in  many  farming  regions  than  in  most  cities. 

Uses  and  functions  of  ground-water.  Ground-water  is  of  vital 
importance  in  the  economy  of  the  earth  and  in  human  affairs,  (i) 
It  is  important  to  plants.  It  dissolves  the  mineral  elements  of  plant 
food  and  carries  them  to  the  roots.  The  amount  of  water  available 
for  plants  is  the  most  important  factor  conditioning  their  life  in  many 
regions.  (2)  Underground  water  supplies  all  springs  and  wells,  the 
sources  from  which  perhaps  three-fourths  of  the  people  of  the  United 
States  obtain  their  water  for  household  use. 


Fig.  115.  Diagram  showing  the  in- 
tricate underground  drainage  which  issues 
in  a  deep-seated  spring.     (Geikie.) 


2C8 


MODIFICATION  OF  LAND   SURFACES 


The  distribution  of  population  in  eastern  United  States  was  influenced  g^ea^ly 
by  running  water  and  natural  springs,  until  modem  methods  of  well-digging  were 
developed.  Absence  of  springs,  and  the  use  for  two  years  of  the  brackish  water  oi 
the  James  River,  were  one  cause  of  the  high  death-rate  in  the  Jamestown  colony. 
A  supply  of  wholesome  water  helped  to  determine  the  location  of  the  Pilgrim 
colony  at  Plymouth,  and  of  the  Puritan  settlement  at  Boston.  Many  of  the 
stockaded  villages  of  the  early  western  frontier  were  so  located  as  to  command  a 
supply  of  water  in  the  event  of  an  Indian  siege.  The  settlement  of  certain  inter- 
stream  areas  in  southern  Wisconsin 
and  in  Illinois  was  delayed  for  years, 
partly  because  of  the  difficulty  and 
expense  of  digging  wells.  In  the  arid 
West,  springs  and  watering  places 
determine  the  location  of  many  vil- 
lages and  farms,  and  influence  the 
course  of  trails  and  roads  (Fig.  ii6). 
Their  location  is  shown  on  many  maps 
for  the  benefit  of  travelers. 

Because  of  the  importance  of 
ground-water  to  plant,  animal, 
and  human  life,  it  is  highly  de- 
sirable that  the  water  table  be 
kept  near  the  surface  of  the 
ground.  It  is  estimated  that  in 
eastern  United  States  it  has 
been  lowered  from  lo  to  40  feet 
over  large  areas  by  cutting  off 
forests  and  by  careless  methods 
of  tillage  which  have  increased 
the  proportion  of  the  rain-water  that  runs  off  over  the  surface.  It  is 
estimated  that  at  least  three-fourths  of  the  shallow  wells  and  springs 
have  failed  in  this  part  of  the  country.  (3)  Ground- waters  bring 
about  important  changes  in  the  character  of  the  rocks  through  which 
they  pass.  These  changes  take  place  slowly,  but  they  are  going  on 
all  the  time. 

OUTFLOWING  WATERS 

Hillside  and  fissure  springs.  Fig.  117  illustrates  two  kinds 
of  springs.  In  the  one,  water  descends  through  a  porous  bed  of 
rock,  c,  to  a  layer,  a,  which  is  compact.  Much  of  the  water  flows 
along  this  layer  until  the  latter  comes  to  the  surface  (out-crops),  and 
there  the  water  issues  as  a  hillside  spring,  s.  The  great  majority  of 
springs  are  of  this  class,  and  most  of  them  are  small.    In  the  other 


Fig.  116.  Map  showing  springs  (by 
circles)  and  roads  in  the  region  of  Flag- 
staff, Arizona.  (From  San  Francisco 
Mountain  Sheet,  U.  S.  Geol.  Surv.) 


FLOWING  WELLS  AND   SPRINGS 


209 


case  (Fig.  117),  the  water  moves  through  the  porous  layer,  b,  under 
pressure,  until  it  reaches  a  crack  which  leads  up  to  the  surface.  If 
the  crack  is  open,  the  water  will  follow  it  up  to  the  surface,  as  at  s\ 
forming  a  fissure  spring.  In  such  a  situation  there  will  be  a  spring 
only  when  the  opening  is  lower  than  the  water  surface  in  the  layer 


Fig.  117.     Diagram  to  illustrate  two  types  of  springs,  as  explained  in  text. 

of  rock  which  carries  the  water.  This  sort  of  spring  is  similar  to  a 
flowing  well  in  principle,  though  in  the  latter  case  the  opening  is  made 
by  man. 

Artesian  wells.  Formerly,  artesian  wells  were  regarded  as  the 
same  as  flowing  wells.  Now,  the  name  "artesian"  often  is  applied  to 
deep,  drilled  wells,  whether  they  flow  or  not.     Fig.  118  illustrates 


Fig.  118.    Diagram  illustrating  the  conditions  necessary  for  flowing  wells 

the  conditions  necessary  for  flowing  wells.  They  are:  (i)  A  porous 
layer  or  bed  of  rock.  A,  under  one  which  is  not  porous,  and  which 
prevents  the  water  from  escaping  upward  until  it  is  penetrated  by  the 
well  hole,  W.  The  porous  bed  must  come  to  the  surface  in  a  region 
which  is  higher  than  the  site  of  the  well;  and  (2)  enough  rainfall  where 
the  porous  bed  comes  to  the  surface  to  keep  that  bed  well  filled  with 


!10 


MODIFICATION  OF  LAND   SURFACES 


water.     Under  these  conditions,  the  water  will  gush  up  (Fig.  119), 
if  a  hole  is  made  down  to  it. 

Flowing  wells  may  be  but  a  few  feet  deep,  or  they  may  be  thousands  of  feet 
deep.  Thus  there  is  one  in  St.  Louis  nearly  4,000  feet  deep,  and  many  in  New 
Jersey  less  than  100  feet  in  depth.  Many  villages  and  small  cities  get  their  water 
from  artesian  wells;  but  great  cities,  such  as  New  York  and  Chicago,  could  not  get 
enough  in  this  way.  Brooklyn  obtains  a  part  of  its  supply  in  this  way,  its  artesian 
wells  furnishing  about  22,000,000  gallons  per  day.     In  parts  of  the  West,  artesian 

waters  are  used  extensively  for  irrigation,  as  well 
as  for  domestic  and  other  purposes. 

In  some  regions  more  wells  have  been  drilled 
than  are  needed,  and  when  not  in  use  (in  many 
cases  this  is  the  greater  part  of  the  time)  the 
water  from  the  flowing  wells  has  been  allowed  to 
run  off  freely.  This  has  reduced  so  greatly  the 
pressure  and  the  amount  of  water  available, 
that  villages  and  cities,  formerly  abundantly 
supplied  from  artesian  wells,  have  been  com- 
pelled to  seek  other  sources  of  supply.  This  is 
the  case,  for  example;  in  some  parts  of  the 
Dakotas.  In  some  of  the  arid  states  where  the 
water  problem  is  critical,  as  in  California,  strict 
laws  exist  to  prevent  the  waste  of  artesian  and 
other  underground  waters. 


Fig.  I  iQ.  An  artesian  well  at 
Lynch,  Nebraska.  Flows  more 
than  3,000  gallons  per  minute. 
(Darton,  U.  S.  Geol.  Surv.) 


Geysers.  Geysers  are  hot  springs 
which  erupt  from  time  to  time  (Fig. 
120).  So  far  as  known,  they  occur  only 
in  a  few  regions  of  recent  volcanic  activ- 
ity—  Yellowstone  National  Park,  New 
Zealand,  and  Iceland.  From  a  few  geysers  water  is  thrown  to  a  height 
of  200  feet  or  more,  by  steam  produced  at  some  point  in  the  geyser 
tube  below  the  top  of  the  water.  It  is  believed  that  hot  volcanic 
rocks  make  the  water  boil,  and  the  expansion  of  the  steam  formed 
causes  the  eruptions.  (How  will  the  cooling  of  the  rocks  affect  the 
frequency  of  eruptions?  What  will  be  the  final  fate  of  existing 
geysers?)     Although  interesting,  geysers  are  of  little  importance. 

Other  hot  springs.  Some  springs  are  warm,  and  others  are  hot. 
Where  spring-water  is  hot,  it  is  in  some  cases  because  it  has  been 
in  contact  with  lava  which  came  up  from  greater  depths  so  recently 
that  it  has  not  yet  become  cold.  In  other  cases  the  heat  may  be 
due  to  chemical  changes  taking  place  beneath  the  surface.  There 
are  more  than  3,000  hot  springs  in  the  Yellowstone  National  Park, 
and  many  others  in  different  parts  of  the  country. 


MINERAL  WATERS 


211 


Mineral  and  medicinal  springs.  All  spring-water  has  some 
mineral  matter  in  solution;  but  a  spring  is  not  commonly  called  a 
mineral  spring  unless  it  contains  (i)  much  mineral  matter,  (2)  mineral 
matter  which  is  unusual  in  spring- water, 
or  (3)  mineral  matter  which  is  conspic- 
uous either  because  of  its  color,  odor, 
or  taste.  Many  mineral  springs  are 
thought  —  and  some  rightly  —  to  have 
healing  properties,  and  so  are  known  as 
medicinal  springs.  Many  of  the  famous 
watering-places  and  resorts  for  invalids 
are  at  hot  mineral  springs.  The  Hot 
Springs  of  Arkansas,  Virginia,  South 
Dakota,  and  Carlsbad  (Bohemia)  are 
examples.  Many  springs  which  are 
charged  with  gases  are  called  mineral 
and  medicinal,  even  though  their  waters 
are  worthless  for  healing  purposes.  In 
191 1  mineral  water  was  sold  from  about 
700  springs  in  the  United  States.  The 
amount  of  water  sold  was  more  than 
67,000,000  gallons,  valued  at  about 
$7,800,000, 

WORK  OF  GROUND-WATER 

Solution.  All  water  which  comes 
out  of  the  ground  has  in  solution  some 
mineral  matter  dissolved  from  the  rock 
through  which  the  water  has  passed. 
Pure  water  does  not  dissolve  mineral 
matter  readily;  but  rain-water  is  not 
pure,  for  it  dissolves  gases  from  the  air, 
and  in  sinking  through  the  soil  takes  up 
the  products  of  plant  decay.     With  these 

impurities  in  solution,  ground-water  dissolves  most  sorts  of  mineral 
matter  more  readily  than  pure  water  would.  The  amount  of  mineral 
matter  brought  to  the  surface  through  springs  is  very  great. 

Much  ground-water  finds  its  way  to  rivers  after  it  seeps  out. 
The  larger  part  of  the  mineral  matter  in  solution  in  rivers  has  come 
from  ground-water  which  has  flowed  to  them.     All  the  rivers  of  the 


Fig.  1 20.  The  Wairoa  Gey- 
ser, New  Zealand.  Shoots  1,500 
feet.  (New  Zealand  Gov't 
Tourist  Dept.) 


212  MODIFICATION  OF  LAND  SURFACES 

earth  are  estimated  to  carry  nearly  five  billion  tons  of  mineral  matter 
to  the  sea  in  solution  each  year.  The  transfer  of  so  much  mineral 
matter  in  solution  from  land  to  sea,  lowers  the  land. 

Some  of  the  mineral  matter  carried  to  the  sea  in  this  way  remains 
in  the  sea-water.  Thus,  most  of  the  salt  which  has  been  carried  to 
the  sea  remains  there,  probably,  to  this  day.  On  the  other  hand, 
much  of  the  mineral  matter  taken  to  the  sea  is  used  by  sea  animals 
(and  some  plants)  for  making  their  shells  and  bones,  and  these  are 
left  on  the  sea-bottom  when  the  organisms  die. 

Caverns  and  cavern  life.  By  the  dissolving  work  of  ground-water,  rock  is 
made  porous.  Small  pores  and  cavities  are  more  numerous  than  large  ones,  but 
some  of  the  openings  made  in  this  way,  such  as  Mammoth  Cave  in  Kentucky  and 
Wyandotte  Cave  in  southern  Indiana,  are  very  large.  Such  caves  occur  chiefly 
in  limestone,  for  this  is  the  most  soluble  of  the  common  rocks. 

A  few  animals  live  in  caves  and  some  of  them  show  peculiar  features.  They 
are  colored  less  brightly  than  their  relatives  above  ground.  This  is  probably 
because  of  the  absence  of  sunlight,  which  seems  to  have  much  to  do  with  producing 
color  in  animals.  Some  cave  animals  have  good  eyes,  some  have  poor  eyes,  and 
some  have  none.  From  these  and  other  facts,  we  infer  that  the  eyes  of  animals 
in  dark  caves  tend  to  disappear.  The  organs  of  touch  are  well  developed  in 
cavern  animals.  In  the  darkness  the  sense  of  touch  is  much  more  useful  than 
sight. 

In  Europe,  certain  caverns  were  the  homes  of  primitive  man,  as  shown  by  the 
human  bones  and  the  tools  which  are  found  in  them.  Here,  too,  are  found  the 
bones  of  large  animals  which  were  killed  for  food  or  fur,  and  taken  to  the  caves. 
On  some  of  the  bones  of  such  animals,  and  on  pieces  of  slate  or  wood,  there  are 
drawings,  some  of  which  are  of  animals  no  longer  living  in  the  region  where  the  caves 
are.  From  this  we  infer  that  the  people  who  lived  in  the  caves  dwelt  there  a  long 
time  ago. 

Deposition.  Ground-water  sometimes  leaves  a  part  of  its  dis- 
solved mineral  matter  in  the  pores  and  cracks  of  the  rocks  through 
which  it  flows.  When  cracks  in  the  rocks  are  filled  or  partly  filled 
by  mineral  matter  deposited  from  solution,  the  fillings  become  veins 
(Fig.  i2i).  Many  ores  of  gold,  silver,  lead,  zinc,  copper,  and  other 
metals,  occur  in  veins.  Originally,  most  of  the  metals  were  scattered 
widely  through  the  rocks.  They  were  dissolved,  and  then  deposited 
by  ground-waters  in  the  cracks  and  openings  w^here  they  are  now 
found.  Thus  ground-water  has  made  the  great  deposits  of  most  ores, 
so  important  to  mankind  (pp.  179-182).  Ground-waters  also  deposit 
mineral  matter  among  particles  of  loose  sediment,  cementing  them 
into  firm  rock. 

Mineral  matter  brought  to  the  surface  by  ground-water  may 


WORK  OF   GROUND-WATER 


21J 


be  deposited  there,  as  the  result  of  various  causes,  (i)  When  water 
evaporates,  the  mineral  matter  dissolved  in  it  is  left  behind.  This 
is  one  reason  why  kettles  in  which  water  is  boiled  become  coated  with 
mineral  matter.  (2)  Certain  gases  dissolved  in  water  help  it  to  dis- 
solve mineral  matter.  If  water  contains  much  gas,  which  later  es- 
capes, as  when  the  water  is  heated,  some  of  the  mineral  matter  in 
solution  may  be  deposited.  (3)  Warm  spring-water  may  give  up 
what  it  holds  in  solution  when  it  cools.  (4)  Microscopic  plants  grow 
in  the  waters  which 
issue  from  some  hot 
springs,  as  in  Yellow- 
stone Park,  and  by 
some  process  not  well 
understood  extract 
mineral  matter  from 
the  water,  and  cause 
it  to  be  deposited. 

Solution  and  deposi- 
tion may  be  going  on  at 
the  same  time,  in  the  same 
place.  Thus  the  original 
material  of  a  buried  shell 
may  be  dissolved  and  car- 
ried away  at  the  same 
time  that  other  material 
is  left  in  its  place,  pre- 
serving the  form  of  the 
shell.  In  the  same  way, 
wood  may  be  replaced  by 
mineral  matter,  giving  rise 
to  petrified  wood,  or  wood 
"  turned  to  stone."     Such 

changes  probably  take  place  slowly,  the  mineral  matter  which  was  in  solution  in 
the  water  replacing  the  woody  matter  as  it  decays. 


Fig.  121.  A  quartz  vein  (the  white  band)  fill- 
ing a  crack  in  much  older  rock.  Muchals  Caves, 
Kincardineshire,  Scotland. 


Mechanical  work.  Mechanical  wear  by  ground-water  is  slight, 
since  ground-water  rarely  flows  in  strong  streams.  Indirectly, 
ground- water  helps  to  bring  about  changes  of  another  sort.  When  the 
soil  on  a  steep  slope  becomes  full  of  water,  its  weight  is  increased  great- 
ly, and  the  water  in  it  makes  it  move  more  easily.  Under  these  cir- 
cumstances, it  sometimes  slides  down.  Such  movements  are  known 
as  slumping  or  sliding.    If  the  slide  is  large,  it  usually  is  called  a 


214 


MODIFICATION  OF  LAND   SURFACES 


landslide  (Fig.  122).     Slumping  is  very  common  on  the  slopes  of 
hUls  composed  of  clay  or  other  loose  matter.     Many  landslides  have 

been  very  destructive. 

In  1903  there  was  a  slide 
on  Turtle  Mountain,  Prov- 
ince of  Alberta,  Canada. 
A  huge  mass  of  earth  nearly 
half  a  mile  square,  and 
probably  400  to  500  feet 
deep,  suddenly  slid  down 
the  steep  face  of  the  moun- 
tain, into  the  valley  below. 
The  length  of  the  slide  was 
about  two  and  a  half  miles, 
and  it  is  estimated  that  the 
time  which  it  took  was  not 
more  than  100  seconds. 
The  hea\y  rainfall  of  the 
preceding  year  had  filled 
the  rock  with  water,  and 
the  earth  tremors  which 
occurred  shortly  before  the 
slide  are  believed  to  have 
hastened  the  catastrophe. 

Water  in  the  soil 
and  subsoil  works  with 
gravity  in  the  ex- 
tremely slow,  down^ 
slope  movement  of 
surface  material.  This 
sort  of  movement  is 
creep  (Fig.  123),  which 
is  usually  too  ^slow  to 
be  seen. 


Fig.  122.    A 
graph  by  Hole.) 


landslide.     (Sketch  from  photo- 


Fig.  123.  A  ravine  near  Crawfordsville,  In- 
diana, showing  trees  leaning  down-slope,  in  part 
because  of  creep.  The  surface  material  creeps 
faster  than  that  below,  tipping  the  trees  toward  the 
axis  of  the  ravine. 


SUMMARY 
From  the  preceding 
paragraphs  it  is  ap- 
parent that  the  exist- 
ence and  work  of  ground-water  are  matters  of  great  importance, 
(i)  Without  water  in  the  soil  most  plants  could  not  live,  and  the 
amount  available  largely  controls  both  the  density  and  the- character 
of  the  vegetation.     (2)  Chiefly  through  its  influence  on  plant  life. 


WORK  OF  RUNNING  WATER  215 

ground-water  helps  to  determine  the  distribution  and  occupations  of 
people.  (3)  Ground-water  is  the  source  of  ail  wells  and  springs. 
Ground-water,  seeping  out,  maintains  the  flow  of  most  streams.  (4) 
Ground- water  may  modify  the  character  of  rocks  in  several  ways: 
(a)  by  removing  soluble  constituents;  (b)  by  depositing  new  mate- 
rial in  rock  cavities;  (c)  by  replacing  old  material  with  new;  and 
(d)  by  favoring  new  chemical  combinations.  These  changes  must 
have  occurred  on  a  vast  scale,  for  ground-waters  have  been  at  work 
for  untold  millions  of  years.  As  a  result,  soils  and  useful  ores  have 
been  accumulated.  (5)  The  mechanical  work  of  ground- water  is 
relatively  unimportant,  but  widespread.  The  creeping  and  slump- 
ing of  surface  material  are  in  some  cases  due  partly  to  ground-water, 

QUESTIONS 

1.  In  order  to  contain  water  constantly,  must  wells  extend  farther  below 
the  surface  of  the  ground  on  hill  tops  or  in  valley  bottoms? 

2.  In  order  to  increase  the  flow  of  water,  dynamite  is  sometimes  exploded  in 
wells.  Why  does  this  in  many  cases  produce  the  desired  effect?  Would  it  be  more 
likely  to  succeed  with  wells  in  hard,  brittle  rocks,  or  soft,  tough  rocks? 

3.  Make  a  diagram  showing  (i)  the  surface  of  the  ground  in  a  hilly  region  con- 
taining a  lake,  a  swamp,  and  a  river,  and  (2)  the  position  of  the  water  table  beneath 
this  surface  (a)  after  continued  rains,  and  (b)  during  a  long  drought. 

4.  What  effect  does  the  irrigation  of  arid  lands  by  water  led  in  ditches  from 
streams  have  on  the  position  of  the  water  table?  How  does  this  affect  the  question 
of  the  acreage  which  may  be  irrigated  in  years  to  come? 

5.  Why  are  the  inscriptions  on  many  old  tombstones  indistinct? 

6.  Describe  the  characteristics  of  a  climate  which  should  (i)  hinder,  and  (2) 
favor  solution  by  ground-water. 


The  Work  of  Streams 

Running  water  is  more  effective  than  wind  in  changing  the  sur- 
face of  the  land  over  which  it  moves,  largely  because  water  is  about 
80  times  heavier  than  air.  The  work  of  running  water  is  also  much 
more  important  than  that  of  ice,  because  water  moves  more  readily 
and  affects  larger  areas.  It  is  true  that  glaciers  have  been  much  more 
extensive  than  now  at  different  times  in  the  past,  but  this  was  the 
case,  so  far  as  known,  only  for  comparatively  short  periods.  On  the 
other  hand,  streams  are  numerous  in  most  lands,  and  have  been  for 
untold  ages.  All  in  all,  running  water  is  more  important  than  all 
other  agents  in  shaping  the  details  of  land  surfaces. 

Streams  modify  land  surfaces  (i)  by  moving  loose  material  to 


2i6  MODIFICATION  OF  LAND   SURFACES 

lower  levels,  much  of  it  to  the  sea,  (2)  by  wearing  their  channels, 
and  (3)  by  depositing  their  excess  loads  in  various  forms.  These 
phases  of  river  work,  together  with  their  topographic  results  and 
some  of  their  human  relations,  are  discussed  below.  The  use  of 
streams,  as  for  commerce,  manufacturing,  and  irrigation,  is  discussed 
in  Chapter  XVI. 

TRANSPORTATION 

Gathering  sediment.  As  rain-water  flows  down  the  slopes  on 
which  it  falls,  it  carries  particles  of  earth  to  the  streams  below.  A 
stream  gets  much  sediment  in  this  way,  if  the  immediate  run-off 
flows  over  bare,  steep  slopes  of  loose  material,  and  little,  if  it  flows 
over  slopes  wxll  covered  with  vegetation,  such  as  grass  land  or  forest. 
Besides  the  sediment  brought  to  it  by  slope  wash,  a  stream  also 
gathers  material  from  its  bed  and  banks. 

A  stream  is  not  a  single,  straightforward  current.  When  water 
runs  swiftly  through  an  open  ditch  or  gutter,  some  of  it  may  be  seen  to 
move  from  sides  to  center,  and  some  from  center  to  sides,  while 
eddies  are  common.  There  are  also  many  subordinate  currents  in 
the  main  current  of  a  river,  and  they  move  in  various  directions. 
Many  of  them  are  caused  by  the  unevenness  of  the  bed  of  the  stream 

(Fig.  124).     Some  of  them 
^  move    upward    and    carry 

sediment  up  from  the  bot- 
tom of  the  stream. 
^  _^  Ground-water  dissolves 

/^/^^a~\Y^ ^y,::^''l^c i  rock   slowly,    and    springs 


T,.  T^.  .•„...,      rr         bring  some  of  this  dissolved 

Fig.  124.     Diagram  to  illustrate  the  effect  ,  . 

of  irregularities,  a  and  b,  in  a  stream's  bed,  on      matter  to  streams  (p.  2ii). 
the  current  striking  them.  Most   dissolved    substances 

are  invisible,  and  remain  in 
the  water  even  after  it  has  become  quiet.  The  amount  of  matter 
carried  to  the  sea  in  solution  each  year  by  all  rivers  (p.  211)  has 
been  estimated  to  be  about  one-third  as  much  as  the  sediment 
carried  by  them. 

Carrying  sediment.  Coarse  materials,  such  as  pebbles,  in  most 
cases  are  rolled  along  the  bottom,  while  fine  materials,  such  as  mud 
and  silt,  are  likely  to  be  carried  in  suspension.  The  behavior  of  the 
fine  sediment  in  suspension  needs  explanation. 

Mud  consists  chiefly  of  tiny  particles  of  rock,  nearly  three  times 
as  heavy  as  water;  hence  they  tend  to  sink  all  the  time.     But  as 


TRANSPORTATION   BY  STREAMS  217 

gravity  brings  them  down,  many  are  caught  by  upward  currents 
(Fig.  124),  and  carried  up  in  spite  of  gravity.  It  is  largely  by  means 
of  these  minor  upward  currents  in  the  main  stream,  that  sediment  is 
kept  in  suspension.  Particles  of  sediment  suspended  in  a  stream  are 
dropped  and  picked  up  repeatedly,  and  the  long  journey  of  any  particle 
is  made  up  of  many  short  ones. 

Amount  of  load.  The  amount  of  sediment  a  stream  carries 
depends  on  (i)  its  swiftness,  (2)  its  volume,  and  (3)  the  amount  and 
kind  of  sediment  which  it  can  get.  Swift  and  large  streams  can 
carry  a  heavier  load  than  slow  and  small  ones.  The  effect  of  velocity 
on  the  carrying  power  of  streams  may  be  seen  in  most  creeks  and 
rivers  which  are  wider  in  some  places  than  in  others.  Where  the 
channel  is  narrow,  the  current  is  swift,  and  here,  in  many  cases, 
all  fine  material  has  been  swept  away,  leaving  only  pebbles  and 
larger  stones  in  the  channel.  Where  the  channel  is  wider,  and 
the  current  slower,  the  bottom  of  the  same  stream  may  be  covered 
with  sand  or  mud.  By  narrowing  the  channel  of  the  Mississippi 
by  making  jetties  near  one  of  its  mouths,  in  1875,  James  B.  Eads 
not  only  prevented  further  deposition  of  sediment  there,  but  forced 
the  river  to  clear  out  its  own  channel.  This  change  permitted 
larger  ocean  vessels  to  reach  New  Orleans. 

The  amount  of  material  which  certain  streams  carry  to  the  sea  has  been 
estimated.  For  a  given  river,  the  estimate  is  made  by  calculating  the  average 
amount  of  water  (in  gallons  or  in  cubic  feet)  discharged  by  it  each  year,  and  then 
determining  the  average  amount  of  sediment  in  each  gallon  or  each  cubic  foot. 
The  Mississippi  River  carries  to  the  Gulf  of  Mexico  an  average  of  more  than  a  mil- 
lion tons  of  sediment  a  day.  It  would  take  nearly  900  daily  trains  of  50  cars,  each 
car  loaded  with  25  tons,  to  carry  an  equal  amount  of  sand  and  mud  to  the  Gulf. 
This  sediment  represents  a  great  loss  to  the  country  (p.  167),  for  most  of  it  would 
make  soil  of  great  fertility,  if  it  were  on  land.  All  the  rivers  of  the  earth  are  carry- 
ing perhaps  40  times  as  much  as  the  Mississippi. 

CORRASION 

How  streams  wear  rocks.  As  already  stated  (p.  216),  streams 
wear  {corrode)  their  channels.  If  the  channel  is  muddy,  the  mov- 
ing water  picks  up  sediment ;  if  sandy  or  gravelly,  sediment  is  rolled 
along  the  bottom.  Many  streams  flow  on  solid  rocks,  and  they 
gather  load  even  from  them.  Rock  exposed  to  water,  as  in  the  bed 
of  a  stream,  decays.  As  it  decays,  it  crumbles,  and  the  crumbled 
parts  are  swept  away  by  a  swift  current.  Again,  the  sand  and 
gravel  rolled  along  by  a  stream  wear  its  bed  even  if  it  is  of  hard 


2l8 


MODIFICATION  OF  LAND   SURFACES 


rock.  Subordinate  currents  sometimes  drive  the  sediment  in  suspen- 
sion against  the  bottom  or  sides  of  the  channel  with  similar  results. 
The  bits  of  sediment  which  a  stream  carries  therefore  become  tools 
(Fig.  125),  with  which  even  hard  rock  is  worn  away.  Clear  water, 
flowing  over  firm,  hard  rock,  wears  the  rock  little.     This  is  shown 


Fig.  125.    The  tools  of  a  river. 
Joe  River,  Washington.     (Tolman.) 


Stream-worn  pebbles  in  the  bed  of  the  St 


by  the  fact  that  in  many  cases  even  large  rivers  flowing  from  lakes 
have  "mossy"  channels.     (Why  do  such  rivers  have  few  tools?) 

Rate  of  erosion.  The  rate  at  which  a  stream  wears  down  the 
surface  over  which  it  flows  depends  largely  on  (i)  its  volume,  and 
this  depends  chiefly  on  the  amount  of  precipitation,  and  on  the 
size  and  topography  of  the  area  draining  to  it;  (2)  its  velocity,  which 
is  determined  chiefly  by  its  slope,  or  gradient,  and  its  volume;  (3) 
the  character  of  its  bed,  especially  the  resistance  of  its  materials;  and 
(4)  the  load  which  the  running  water  carries.  To  work  most  effec- 
tively, the  water  must  have  tools  enough  to  enable  it  to  cut  rapidly, 
but  not  so  many  that  the  energy  expended  in  moving  them  retards 
its  flow  seriously.  Since  the  factors  named  above  vary  greatly, 
the  rate  at  which  the  land  is  being  worn  down  is  very  unequal  in 
different  places.  The  average  rate  of  wear  for  the  United  States 
is  thought  to  be  about  i  inch  in  760  years;  but  the  rate  varies  from 


RIVER  VALLEYS   IN  HISTORY 


219 


an  average  of  i  inch  of  reduction  in  about  440  years  in  the  Coloiado 
Basin,  to  i  inch  in  about  3,900  years  in  the  basin  of  the  Red  River  of 
the  North  (Fig.  126), 

FEATURES  DEVELOPED  BY  STREAM  EROSION 

River  Valleys 

The  depressions  in  which  rivers  flow  are  their  valleys,  and  in 
the  making  of  valleys  streams  have  been  the  chief  agents. 

River  valleys  centers  of  human  activity.  Most  of  the  great 
valley  lowlands  of  middle  latitudes  are  settled  densely,   because 


Fig.  1 26.  Rates  c :  land  reduction  by  stream  erosion  in  the  United  States. 
The  figures  are  the  approximate  number  of  years  required  for  one  inch  of  reduction^ 
(Dole  and  Stabler,  U.  S.  Geol.  Surv.) 


of  their  fertile  soils,  favorable  topography,  and  facilities  for  com- 
munication. Probably  more  than  one-fourth  of  the  people  of  east- 
ern United  States  live  on  alluvial  lands. 

The  valleys  of  the  United  States  have  been  sought  out  for  set- 
tlement from  the  beginning  of  its  history.  New  York  history  began 
at  the  mouth  of  the  Hudson,  Pennsylvania  history  in  the  valley 
of  the  Delaware,  and  that  of  Virginia  on  the  banks  of  the  James. 
Later,  various  valleys  became  highways  of  expansion  toward  the 
interior.  The  overflow  from  the  settlements  of  the  coastal  low- 
lands of  Massachusetts  passed  over  the  rocky  and  infertile  uplands 


220 


MODIFICATION  OF  LAND   SURFACES 


to  the  west,  to  the  inviting  bottom  lands  and  terraces  of  the  Con- 
necticut Valley.  As  years  passed,  this  great  valley  led  settlers 
northward  into  New  Hampshire  and  Vermont.     The  Ohio  Valley 

was  one  of  the  first 
sections  of  the  inte- 
rior to  be  settled,  and 
for  many  years  the 
Ohio  River  was  a 
main  highway  of 
westward  expansion. 
The  upper  Rio  Grande 
Valley  guided  settlers 
northward  from  Mex- 
ico into  the  United 
States.  The  Platte 
Valley  directed  many 
fur  traders  and  trap- 
pers across  the  Great 
Plains;  it  was  fol- 
lowed by  the  Mor- 
mons on  their  way  to 
Utah;  along  it  ran  the 
Oregon  Trail  and  the 
first  trans-continental  railroad;  and  it  was  the  greatest  gateway  into 
Nebraska  when,  in  the  fifties,  the  latter  began  to  be  settled.  Many 
other  examples  of  the  part  which  valleys  have  played  in  expansion 

J,  and  settlement  might  be 

o -. -^ , 

given. 

The  larger  rivers  of 
eastern  United  States 
were  long  the  great  high- 
ways of  trade  and  travel. 
Much  of  the  Interior 
depended  largely  on  the 
Mississippi  and  its  tribu- 
taries as  outlets  to  market,  before  the  building  of  railroads  (p-  274). 
In  the  future,  the  larger  rivers  of  the  United  States  probably  will 
be  used  more  than  now  for  transportation  (p.  287). 

Many  valleys  are   grown-up  gullies.     Many  valleys  are  en- 
larged gullies.    A  gully  started  during  one  shower  (Fig.  127)  is  ma.de 


Fig.  127.     A  gully  made  by  a  single  shower. 


Fig.  1 28.    Diagram  illustrating  how  one  gully 
takes  others  as  a  result  of  growth. 


FORMATION  AND  GROWTH  OF  VALLEYS 


221 


deeper,  wider,  and  longer  by  the  next.     As  the  result  of  repeated 
showers  year  after  year  and,  in  many  places,  repeated  meltings 


Fig.  1 29.     Gullying  in  southwestern  Iowa.     (Iowa  State  Drainage,  Waterways, 
and  Conservation  Commission.) 


of  snows,  the  gully  grows  to  be  a  ravine,  and  later  a  valley.  Not 
all  gullies,  however,  become  valleys.  Many  gullies  may  start  on 
one  slope,  but  as  they 
grow,  some  are  so 
widened  as  to  take  in 
others  (Fig.  128),  and 
the  number  is  reduced. 
Few  gullies  become 
ravines,  fewer  still  be- 
come small  valleys, 
and  the  number  of 
valleys  which  attain 
great  length  is  very 
small. 

Growth  of  gullies 
should  be  prevented. 
Much  land  in  the 
United  States  has  been 
ruined  and  much  more 
injured,  by  gullies. 
There  are  many  exam- 


Fig.  130.     Brush  dams  built  to  check  erosion  in 
the  southern  Appalachians. 


pies  of  such  land   in  the  southern  Appalachians,  where,  on   bare 
surfaces,  gullies  form  and  grow  rapidly  because  the  slopes  are  steep, 


222  MODIFICATION  OF  LAND   SURFACES 

the  rainfall  heavy,  and  much  of  the  surface  material  is  eroded  easily. 
Surfaces  of  this  sort  should,  as  a  rule,  be  given  over  to  the  growth  of 
forests.  But  serious  gullying  is  by  no  means  confined  to  mountain 
areas  (Fig.  129),  and  the  problem  of  checking  the  growth  of  gullies 
is  country- wide.  One  of  the  best  ways  of  stopping  their  growth  is  by 
filling  them  with  brush  (Fig.  130). 

How  valleys  get  streams.  Water  commonly  flows  in  gullies 
only  when  it  rains  or  when  snow  melts,  and  for  a  short  time  after- 
ward.    But  many  valleys  made  from  guUies  have  permanent  streams, 

so  that  they  are  being 
made    larger    all    the 
time. 
I  When  a  valley  has 

been  deepened  so  that 
its  bottom  is  below  the 

„.  T^..  ,      .  J      .  ground- water    surface, 

tig.  131.     Diagram  snowing  ground-water  sur-      ° 

face;  a,  the  ground-water  surface  in  wet  weather,  ground-water  seeps  or 
and  b,  in  times  of  drought.  When  a  valley  has  been  flows  into  it,  and  forms 
cut  below  a,  there  will  be  a  stream  in  wet  weather,  cfrt^om       Tn  V\ct 

but  it  will  go  dry  in  time  of  drought.  When  the  val-  ^  siream.  in  r  ig.  1 3 1 , 
ley  bottom  is  below  b,  the  stream  will  be  permanent,      a  represents  the  water 

surface  in  wet  weather, 
and  b  the  water  surface  in  dry  weather.  The  valley  whose  cross- 
section  is  shown  by  i  does  not  have  a  stream  fed  by  ground-water; 
the  valley  2  has  a  small  stream  in  wet  weather;  while  the  valley  3  has 
a  permanent  stream,  because  its  bottom  is  below  the  ground-water 
level  of  dry  times. 

Streams  which  are  fed  by  lakes,  and  streams  which  flow  from 
snow-  and  ice-fields  which  last  from  year  to  year,  do  not  depend 
on  ground-water,  though  in  most  cases  they  receive  it. 

The  deepening  of  valleys.  Swift  streams  remove  material  from 
their  beds  and  so  make  their  valleys  deeper,  but  many  slow  streams 
deposit  more  sediment  than  they  take  away,  and  so  make  their  valleys 
shallower.  Many  streams  deepen  their  valleys  in  their  upper  courses 
where  their  waters  are  swift,  while  they  make  them  shallower  in 
their  lower  courses  where  the  flow  is  sluggish.  As  a  stream  deepens 
its  valley,  the  gradient  becomes  less,  and  the  stream  flows  more  and 
more  slowly.  In  time,  every  swift  stream  will  cut  its  channel  down 
until  its  gradient  is  low  and  its  current  sluggish.  A  stream  cuts  the 
lower  end  of  its  channel  down  to  about  the  level  of  the  lake,  sea,  or 
river  into  which  it  flows,  but  the  channel  rises  from  its  lower  end  to 


FORMATION  AND   GROWTH  OF  VALLEYS 


223 


its  head.     The  lowest  level  to  which  a  stream  can  reduce  its  basin  is 
base-level. 

The  widening  of  valleys.  Valleys  are  widened  in  many  ways, 
among  them  the  following:  (i)  A  stream  may  flow  against  one 
side  of  its  channel  with  such  force  as  to  undercut  the  slope  above. 
Slow  streams  are  more  likely  to 
widen  their  valleys  in  this  way 
than  swift  ones,  because  they  are 
turned  more  easily  against  their 
banks  by  obstacles  in  the  channels. 
(2)  Rain-water  flowing  down  the 
slopes  of  a  valley  carries  earthy 
material  with  it.  This  wddens  the 
valley,  by  slowly  wearing  back 
its  slopes.  (3)  The  loose  matter 
which  lies  on  the  slopes  of  a 
valley  creeps  slowly  downward, 
especially  when  wet.  It  may 
also  slump  down  steep  slopes.  In 
these  and  other  ways,  all  val- 
leys are  being  widened  all  the 
time. 

After  streams  have  cut  their 
valleys  down  to  low  gradients, 
they  make  flats  in  their  bottoms, 
by  side-cutting  (Fig.  132).  These 
flats  are  below  the  level  of  the 
surface  in  which  the  valleys  lie, 
and  may  become  very  wide  (Fig. 
133).  Thus  the  Mississippi  River 
at  Memphis  has  a  flat  about  35 
miles  wide.  Most  valley  flats  increase 
regularly  down  stream  (Why?). 

The  lengthening  of  valleys.  The  headward  growth  of  a  gully 
is  due  chiefly  to  erosion  by  the  water  which  flows  into  its  upper 
end.  The  head  of  a  gully  advances  in  the  direction  of  greatest 
wear,  and  this  is  rarely  in  a  straight  line.  Most  valleys  are  therefore 
crooked  from  the  outset. 

The  headward  growth  of  a  valley  normally  continues  until  the 
wear  of  the  water  flowing  into  its  upper  end  is  equaled  by  the  wear 


Fig.  132.     Diagrams    of    a 
making  a  flat  by  side  cutting. 


river 


in  width    more    or   less 


224 


MODIFICATION  OF  LAND   SURFACES 


of  the  water  flowing  from  the  same  divide  (water-parting)  in  the 
opposite  direction.     The  divide  is  then  permanent  (Fig.  134). 

Valleys  are  not  all  grown-up  gullies.     Not  all  valleys  were 
formed  by  the  growth  of  gullies.     A  vast  area  in  northern  North 


Fig.  133.  A  wide  valley  flat.  Milk  River,  near  the  Montana-Alberta  bound" 
ary.     (From  photograph  by  U.  S.  Geol.  Surv.) 

America,  for  example,  once  was  covered  by  a  sheet  of  snow  and 
ice.  Most  of  the  rivers  which  had  existed  in  this  area  ceased  to 
flow  while  the  ice  lay  on  the  land.     Many  of  their  valleys  were 

filled,  at  least  in  places,  by  the  drift 
which  the  ice  left  when  it  melted, 
and  so  great  areas  were  left  without 
well-defined  valleys.  The  melting 
ice,  however,  supplied  much  water, 
and  this  flowed  along  the  lowest 
lines  of  descent  which  it  could  reach, 
and  made  valleys  along  those  lines. 
Valleys  made  by  such  waters  may 
have  permanent  streams  at  the  start,  since  they  do  not  depend  on 
ground-water. 

Again,  the  melting  of  the  ice  left  many  lakes  in  the  hollows  of 
the  land  it  had  covered,  and  the  rainfall  of  the  region  was  great 
enough  to  make  many  of  them  overflow.     When  a  lake  overflows, 


Fig.  134.  Diagram  of  a  divide. 
The  crest  of  the  divide  (at  A)  is  per- 
manent if  the  conditions  of  erosion 
are  the  same  on  the  two  sides.  Rain- 
fall may  lower  it,  but  cannot  shift 
its  position  horizontally. 


I 


STAGES  OF  EROSION 


225 


the  outgoing  water  follows  the  lowest  line  of  descent,  and  cuts  out 
a  valley.  In  these  ways,  rivers  soon  were  formed  on  the  surface 
from  which  the  ice  melted. 

Valley  and  river  systems.  Most  valleys  are  joined  by  many 
smaller  valleys.  The  reason  is  simple.  The  erosion  of  the  slopes 
of  valleys  by  the  water  flowing  from  them  to  the  valley-bottoms  is 
greater  along  some  lines  than  others  (Why?),  and  tributary  gullies 
are  started,  which,  growing  in  the  same  way  as  the  parent  valleys, 
may  come  to  have  permanent  streams.  These  tributary  valleys  of  the 
first  generation  come  to  have  branches,  and  the  process  may  go  on 
until  a  network  of  watercourses  affects  the  surface. 

A  valley  and  its  tributaries  constitute  a  valley  system.  A  stream 
and  its  branches  form  a  river  system,  and  the  area  drained  by  a  river 
system  is  a  drainage  basin. 

Stages  in  the  history  of  valleys  and  streams.  Valleys  grow  in 
size  as  they  advance  in  years.  When  a  valley  is  young,  it  is  narrow 
and  its  slopes  are  steep.  If  the  land  is  high,  the  valley  may  have  a 
steep  gradient,  in  which  case  it  soon  becomes  deep.  Its  cross-section 
is  then  somewhat  V-shaped  (Fig. 
135,  i),  and  its  tributaries  are  short. 
A  mature  valley  is  wider  (Fig.  135,  2), 
its  slopes  in  most  cases  are  gentler, 
and  its  tributaries  are  longer  and 
older.  An  old  valley  is  wide,  and 
has  a  broad  flat  and  a  low  gradient 

(Fig.  135,  3)- 

A  stream  also,  as  well  as  its  val- 
ley, passes  from  youth  to  maturity, 
and  from  maturity  to  old  age.     In 

its  youth,  it  is  likely  to  be  swift,  unless  it  flows  through  low  land. 
In  maturity,  it  flows  less  swiftly  and  more  steadily,  and  when  it 
reaches  old  age,  it  winds  slowly  through  its  wide  plain.  Even  an  old 
stream,  however,  may  take  on  the  vigor  of  youth  when  in  flood. 

The  terms  youth,  maturity,  and  old  age  may  be  applied  to  river 
systems  as  well  as  to  single  rivers.  Every  river  system,  aided  by 
weathering,  has  entered  on  the  task  of  carrying  to  the  sea  all  the  land 
of  its  basin  which  is  above  base-level.  So  long  as  the  river  system  has 
the  larger  part  of  its  task  before  it,  it  is  young.  When  the  main  valley? 
have  become  wide  and  deep,  and  the  areas  of  upland  have  been  well 
cut  up  by  valleys,  the  river  system  is  said  to  have  reached  maturity. 


Fig.  135.  Diagram    showing 

changes  in  the  shape  of  a  valley  as 
it  advances  from  youth  to  old  age. 
I  =  youth;  3  =  old  age.  The 
material  in  which  the  valley  is  cut 
is  all  of  the  same  character. 


22b 


MODIFICATION  OF  LAND   SURFACES 


When  the  task  of  reducing  its  drainage  basin  to  base-level  is  nearing 
completion,  the  river  system  has  reached  old  age. 

The  topography  of  a  drainage  basin  is  youthful  when  its  river 
system  is  youthful,  mature  when  its  river  system  is  mature,  and 


Fig.  136.     Diagram  of  an  area  in  a  youthful  stage  of  erosion.    The  area  is 
some  distance  irom  the  sea.     The  bottom  of  the  diagram  represents  sea-level. 


Fig.  137.  Diagram  showing  mature  topography  in  a  region  situated  some 
distance  from  the  sea.  The  bottom  of  the  diagram  is  sea-level.  The  area  shown 
in  Fig.  136  will  in  time  resemble  closely  the  present  appearance  of  this  area. 


Fig.  138.  Diagram  showing  old  topography  in  a  region  situated  some  distance 
from  the  sea.  The  bottom  of  the  diagram  is  sea-level.  Unless  the  land  is  elevated, 
the  areas  represented  in  the  two  preceding  figures  will  finally  closely  resemble  this 


area. 


old  when  its  drainage  is  old.  In  an  area  of  youthful  topography, 
much  of  the  surface  has  not  yet  been  much  changed  by  erosion 
(Fig.  136),  and  the  surface  may  be  ill-drained.  In  an  area  of  mature 
topography,  much  of  the  surface  has  been  reduced  to  slopes  by  erosion 


STAGES  OF  EROSION  227 

(Fig.  137),  and  is  well-drained;  while  an  area  of  old  topography  is  one 
which  has  been  brought  down  to  general  flatness  by  erosion  (Fig.  138). 
When  an  area  is  worn  as  low  as  running  water  can  bring  it,  it 
is  a  base-level  plain.  As  streams  wear  the  land  toward  base-level, 
they  flow  on  diminishing  gradients.  Because  of  this,  their  velocity 
and  therefore  their  erosive  power  decrease  constantly.  In  other 
words,  an  area  approaches  base-level  more  and  more  slowly  the 
nearer  it  gets  to  it,  and  it  may  take  as  long  to  wear  away  the  last 
few  feet  above  base-level  as  it  did  all  the  other  hundreds  or  thousands 


Fig.  139.    A  monadnock  on  a  peneplain.    Tower,  Minnesota.     (Mead.) 

of  feet  that  once  lay  above.  Few,  if  any,  areas  have  been  absolute- 
ly base-leveled.  The  time  required  is  enormous,  and  before  the 
task  is  completed,  an  area  is  likely  to  be  elevated  with  reference 
to  sea-level,  and  the  quickened  rivers  started  upon  the  task  of  again 
reducing  the  elevated  land  to  base-level.  But  many  areas  have 
been  nearly  base-leveled.  Such  plains  are  peneplains  (almost  plains). 
Above  their  otherwise  nearly  level  surface,  occasional  elevations  may 
rise  abruptly.  These  elevations,  known  as  monadnocks  (Fig.  139), 
owe  their  existence  to  (i)  the  greater  resistance  of  their  rocks,  or 
(2)  a  favorable  position  among  drainage  lines.  The  time  required 
for  reducing  a  drainage  basin  to  a  base-level  plain  is  a  cycle  of  erosion. 
As  implied  above,  cycles  of  erosion  commonly  are  brought  to  an 
end  by  relative  uplift  of  the  land  before  they  are  completed. 

The  terms  youth,  maturity,  and  old  age,  as  used  in  geography, 
apply  to  stages  of  development,  and  not  to  periods  of  years.  Thus 
a  small  river,  working  on  soft  material,  may  bring  its  valley  to  old 
age  in  less  time  than  that  required  for  a  large  stream,  opposed  by 
resistant  rocks,  to  bring  its  valley  to  maturity. 


228  MODIFICATION  OF  LAND  SURFACES 

Influence  of  stage  of  erosion  on  human  activities.  The  den- 
sity of  population  of  a  region  and  the  condition  and  activities  of 
its  people  are  influenced  greatly  by  the  stage  which  it  has  reached 
in  its  topographic  development.  Many  young  rivers  are  inter- 
rupted by  falls  and  rapids  (p.  230)  which  afford  water  power  for 
manufacturing,  but  interrupt  or  prevent  navigation.  Many  young 
rivers,  too,  are  not  available  for  commerce  partly  because  they 
flow  in  narrow  valleys,  far  below  the  level  of  the  surrounding  coun- 
try. In  parts  of  western  United  States,  it  is  also  impracticable  to  lift 
the  waters  of  such  streams  to  the  neighboring  uplands  for  purposes 
of  irrigation.  Thus  the  waters  of  the  Colorado  River  can  be  used 
for  irrigation  only  in  the  upper  part  of  the  river  system,  or  below 
the  Grand  Canyon,  and  the  larger  irrigation  projects  of  southern 
Idaho  are  related  definitely  to  breaks  in  the  walls  of  the  deep  canyon 
of  the  Snake  River.  Again,  very  deep  valleys  may  make  travel 
across  their  courses  almost  impossible.  In  such  cases,  places  where 
the  valleys  can  be  crossed  may  have  all  the  importance  of  mountain 
passes,  controlling  the  courses  of  trails  and  roads.  The  Denver  and 
Rio  Grande  Railroad  crosses  the  Green  River  in  eastern  Utah  where 
there  is  a  gap  in  the  canyon  wall,  a  gap  that  earlier  fixed  the  course 
of  the  Spanish  Trail.  Roads  may  run  in  any  direction  over  young 
plains  whose  valleys  are  shallow.  Nearly  all  the  land  of  such  plains 
can  be  farmed,  so  far  as  topography  is  concerned.  The  poorly 
drained  inter-stream  flats  may  require  ditching  or  tile  draining, 
however,  as  in  parts  of  Iowa  and  Illinois. 

Where  relief  is  great,  early  maturity  is  least  favorable  to  most 
human  activities.  The  larger  rivers  may  be  navigable,  but  most  of 
their  tributaries  are  likely  to  have  steep  gradients,  with  falls  and 
rapids.  At  this  stage,  run-off  is  at  a  maximum,  and  streams  are  most 
subject  to  floods.  Many  of  the  larger  rivers  are  crossed  at  ferries 
and  fords,  for  bridges  are  hard  to  maintain.  Good  sites  for  river  towns 
may  be  few.  Wagon  roads  and  railroads  follow  the  narrow  ridges 
between  the  valleys,  or  the  flats  of  the  larger  streams.  Farming  is 
difficult  on  the  steep  valley  slopes,  where  soils  are  likely  to  be  thin 
and  easily  washed  away.  In  general,  the  population  of  such  regions 
is  sparse  and  non-progressive,  having  little  contact  with  the  outside 
world.  Mineral  deposits  or  other  special  resources  may  create  in- 
dustrial centers,  whose  progress  serves  to  emphasize  the  backward- 
ness of  the  region  as  a  whole.  These  conditions  are  illustrated  in 
parts  of  the  Cumberland  and  Alleghany  plateaus  (p.  173). 


STAGE  OF   EROSION  AND   HUMAN  ACTIVITIES    229 

Old  rivers  are,  as  a  rule,  free  from  rapids  and  falls,  and  in  most 
cases  have  gradients  so  gentle  that  they  do  not  afford  good  water 
power.  While  these  conditions  favor  navigation,  the  latter  may 
be  interfered  with  by  sand  bars  (p.  237)  and  the  shifting  and  crooked 
courses  of  the  channels.  Much  of  the  land  of  the  broad  flood-plains 
of  old  rivers  is  swampy  and  of  little  use  until  drained,  but  is  then  of 


Fig.  140.    The  canyon  of  the  Yellowstone.     (Hillers,  U.  S.  Geol.  Surv.) 


great  fertility  (Why?).  While  floods  are  most  numerous  in  valleys 
whose  slopes  are  steep,  they  are  more  likely  to  be  disastrous  to  prop- 
erty on  the  broad,  low  flats  of  older  rivers,  such  as  the  lower  Mississippi 
(p.  237).  On  the  gentle  inter- valley  slopes  of  an  old  area,  the  soils 
are  likely  to  be  deep  (Why?);  their  fertihty  depends  chiefly  on  the 
character  of  the  underlying  rock.  The  area  of  land  which  can  be 
farmed  is,  as  a  rule,  much  greater  in  topographic  old  age  than  in  ma- 
turity. On  peneplains,  as  on  youthful  plains  of  low  relief,  travel  is 
easy  in  all  directions.  Wagon  roads  and  railroads  are  not  confined 
to  certain  courses  by  topography. 


230 


MODIFICATION  OF  LAND  SURFACES 


Canyons  and  gorges.  Valleys  which  are  narrow  and  deep 
often  are  called  gorges  if  small,  and  canyons  if  large.  The  Colorado 
Canyon  is  the  greatest  canyon  known.  Its  depth  is  about  a  mile,  and 
it  is  eight  to  ten  miles  wide  at  the  top.  Its  sides  are  step-like,  because 
of  the  unequal  hardness  of  the  rock  of  the  canyon  walls.  The  harder 
strata  are  the  cliff-makers.  The  Yellowstone  (Fig.  140),  Snake,  and 
Columbia  rivers  have  wonderful  canyons  in  some  parts  of  their 
courses,  and  so  nas  the  Arkansas  River  where  it  flows  through  the 

Rocky  Mountains. 
The  canyons  of  many 
smaller  and  less  well- 
known  rivers  are  al- 
most equally  striking. 

A  narrow  valley  means 
that  the  processes  which 
have  made  it  deep  have 
outrun  the  processes  tend- 
ing to  make  it  wide.  Val- 
leys are  deepened  rapidly 
when  their  gradients  are 
high  and  their  streams 
strong.  They  are  widened 
slowly  (i)  when  the  climate 
is  arid,  so  that  there  is  little 
slope  wash,  (2)  when  the  stream  is  so  swift  that  it  does  not  meander,  and  (3)  when 
the  material  of  the  sides  is  such  that  it  will  stand  with  steep  slopes.  Therefore 
(i)  great  altitude,  (2)  arid  climate,  (3)  swift  streams,  and  (4)  rock  which  will 
stand  in  steep  slopes,  favor  the  making  of  canyons.  In  other  words,  young 
valleys  in  plateaus  and  mountains  (as  in  western  United  States)  are  likely  to  be 
canyons.     (How  can  there  be  large,  strong  streams  in  dry  regions?) 

Some  of  the  ancient  cliff-dwellers  made  their  homes  in  the  recesses  of  canyon 
walls  (Fig.  141),  probably  because  these  positions  could  be  defended  easily. 

Canyons  must  change  into  valleys  of  another  type,  for  the  stream 
in  the  canyon  will  in  time  cut  down  to  its  base-level.  The  valley 
will  then  stop  growing  deeper,  but  widening  will  still  go  on,  and  the 
narrow  valley  will  become  so  wide  that  it  will  cease  to  be  a  canyon. 

Rapids  and  falls.  The  bed  of  a  stream  may  be  steeper  at  some 
points  than  at  others,  and  there  the  stream  flows  more  rapidly.  The 
quickened  flow  constitutes  a  rapids;  or,  if  the  water  in  a  stream's  bed 
drops  over  a  cliff,  it  makes  a  waterfall  (Fig.  142).  Waterfalls  and 
rapids  are  important  chiefly  because  they  render  the  power  of  the 
streams  available  to  man  for  purposes  of  manufacturing,  lighting, 


Fig.  141.     Cliff  dwellings,  southwestern  Colorado. 


RAPIDS  AND   FALLS 


231 


transportation,  etc.  (p.  288).  Many  electric  railroads  and  many 
industries  depend  for  power  on  electricity  developed  by  falls  and 
rapids,  and  railroads  and  fac- 
tories of  all  sorts  are  likely  to 
depend  on  this  sort  of  power 
still  more  largely  in  the  future. 
Rapids  and  falls  interfere  with 
navigation,  or  prevent  it  alto- 
gether (p.  228). 

Waterfalls  come  into  existence  in 
various  ways.  A  river  flowing  on  the 
high  gradient  shown  in  Fig.  143  is 
likely  to  be  an  eroding  river.  It  will 
wear  its  channel  faster  at  A ,  where  the 
rocks  are  soft,  than  just  above,  where 
they  are  hard,  with  the  result  shown 
in  Fig.  144.  The  continued  wear  of 
the  water  in  such  a  case  would  cause 
the  rapids  at  A  (Fig.  144)  to  become 
steeper,  and  in  time  the  descending 
water  would  become  a  fall  (Fig.  145). 
In  this  case,  the  rapids  and  falls  de- 
pend on  inequalities  of  hardness  in  the 
bed  of  the  strcatn.  This  is  a  common 
way  in  which  falls  and  rapids  origi- 
nate. A  landslide  or  lava  flow  may 
form  a  dam,  over  which  the  water 
falls  or  flows  in  rapids.  Most  of  the 
waterfalls  of  the  United  States  are 
due  to  glaciation  (pp.  256,  265). 

Falls  and  rapids  are  undergoing 
constant  change,  although  the  change 
is  usually  very  slow.  Many  falls  are 
moving  slowly  up-stream,  because  the 
water  undermines  the  hard  layer  of 
rock  over  which  it  drops  (Fig.  145). 
As  a  fall  moves  up-stream,  it  becomes 
lower  in  many  cases  (Fig.  145).  It  is 
clear  that  such  falls  will  disappear  if 
they  recede  far  enough.     If  the  hard 

rock  over  which  the  water  drops  is  in  the  position  shown  in  Fig.  146,  the  fall 
will  not  recede,  though  it  will  become  lower,  and  will  disappear  when  the  stream 
cuts  down  to  base-level,  where  the  fall  is.  (What  would  be  the  effect  of  re-eleva- 
tion of  the  basin?)  Rapids  and  falls  are  temporary  features  of  streams,  and,  like 
canyons,  are  marks  of  youth.  In  time,  therefore,  all  existing  rapids  and  water- 
falls will  disappear. 


Fig.  142.     Falls  of  the  Black  River, 
Wisconsin.     (Smith,  Wis.  Geol.  Surv.) 


232 


MODIFICATION  OF  LAND  SURFACES 


Narrows.  Many  valleys  are  narrow  where  they  cross  a  tilted 
layer  of  hard  rock.  Such  a  place  in  a  valley  is  a  narrows,  or  water' 
gap  (Fig.  147).  The  Delaware  Water-Gap  through  Kittatinny 
Mountain  (Pa.-N.  J.)  is  a  well-known  example. 


Fig.  143- 


Fig.  144. 


Fig.  145. 

Figs.  143,  144,  145.  Diagrams  to  illustrate  the  development  and  extinctioL 
of  a  waterfall. 

Why  will  the  waterfall  cease  to  retreat  up-stream  when  it  reaches  C-B,  Fig. 
145?    What  changes  will  occur  after  it  reaches  this  place? 


Narrows  sometimes  serve  as  gateways  through  mountains,  and  so  control  lines 
of  travel.  The  narrows  of  Wills  Creek  in  Wills  Mountain,  Maryland,  may  serve 
as  an  example.  In  the  early  days  of  American  history,  Fort  Cumberland  was 
built  at  this  narrows  to  guard  the  important  pass  through  the  mountains,  and 
Washington's  and  Braddock's  roads  ran  west  through  it.  At  the  present  tim^e,^  the 
Cumberland  National  Road  (Fig.  215)  and  an  important  railway  make  use  oi  it. 


PIRACY  AMONG  RIVERS 


2^3 


Accidents  to  streams.  Streams  are  subject  to  many  accidents. 
If  the  land  through  which  they  flow  sinks  so  that  its  slope  is  reduced, 
they  flow  less  rapidly,  or  may  even  cease 
to  flow.  If  the  lower  end  of  a  valley 
sinks  below  sea-level,  the  sea-water 
enters  and  forms  a  bay,  drowning  the 
lower  end  of  the  river  and  its  valley. 
If  the  streams  along  a  coast  end  in 
bays,  we  infer  that  the  coast  has  sunk, 
and  that  its  rivers  and  valleys  have 
been  drowned.  Thus  Delaware  Bay  and 
Chesapeake  Bay  are  drowned  valleys. 

If  the  basin  of  an  old  stream  is  raised  so  that  the  gradient  of  the 
stream  becomes  greater,  its  velocity  is  increased,  and  it  again  takes 
on  the  character  of  youth.    Such  streams  are  said  to  be  rejuvenated. 


Fig.  146.    Diagram  of  water- 
falls develooed  on  vertical  beds. 


Fig.  147.    Lower  Narrows  of  the  Baraboo  River,  Wisconsin.     The  valley 
widens  beyond  the  gap,  the  same  as  in  the  foreground. 

If  by  headward  growth  one  valley  reaches  and  enters  another 
where  the  latter  is  at  a  higher  level,  it  may  steal  the  water  which  other- 
wise would  flow  down  the  higher 
valley   (Figs.  148  and   149).    The 
stream   which    steals    is   a    pirate. 
The  stream  stolen  is  diverted,  and 
the  stream  which  has  lost  its  upper 
water  is  beheaded.     Piracy  has  been 
rather  common  among  rivers,  espe- 
cially in  mountain  regions.     In  the 
Figs.  148,   149.     Diagrams  to     Appalachian    region,   for   example, 
illustrate  stream  piracy.  there  are  few  large   streams  which 


234 


MODIFICATION  OF  LAND   SURFACES 


have  not  either  increased  their  waters  by  piracy,  or  suffered  loss  by 
the  piracy  of  others.  Piracy  is  favored  by  inequahties  of  hardness, 
for  streams  which  do  not  cross  hard  rock  deepen  their  channels 
more  readily  than  those  which  do  (Fig.  150). 

When  a  stream  is  diverted  from  a  narrows,  the  water-gap  becomes 
a  wind-gap.  Wind-gaps  are  common  in  most  mountain  regions 
which  have  advanced  to  late  maturity.  Cumberland  Gap,  in  the 
southeastern  corner  of  Kentucky,  is  an  example.     It  afforded  many 


Fig.  150.  A  case  of  stream  piracy  in  Pennsylvania.  The  upper  part  of  the 
present  Wiconisco  Creek  formerly  was  tributary  to  Deep  Creek,  joining  the  latter 
at  "A."     (From  Millersburg  and  Lykens,  Pennsylvania,  Sheets,  U.  S.  Geol.  Surv.) 

What  enabled  Wiconisco  Creek  to  behead  Deep  Creek?  What  was  the  prob- 
able origin  of  the  mountain  gap  at  "B''?  Is  future  piracy  likely  to  occur  in  this 
region?     Why? 

of  the  early  emigrants  the  best  route  across  the  mountains,  and  during 
the  last  quarter  of  the  eighteenth  century  probably  more  than  300,000 
people  passed  through  it  to  settle  in  the  West.  The  many  wind-gaps 
of  the  Blue  Ridge  Mountains  were  important  in  the  early  westward 
movement  of  population,  and  again  in  the  campaigns  of  the  Civil  War. 


DEPOSITION  BY  STREAMS 

Causes  of  deposition.  Streams  may  become  overloaded  in 
various  ways,  and  so  be  forced  to  deposit  their  excess  sediment: 
(i)  Their  carrying  power  may  be  reduced  by  a  decrease  of  gradient. 
The  change  may  take  place  suddenly,  as  at  the  base  of  a  steep  slope, 
or  it  may  take  place  slowly,  as  a  stream  flows  through  a  valley  whose 
slope  becomes  gradually  less.      (2)    Their  carrying  power  may  be 


WHY  STREAMS  DEPOSIT 


235 


diminished  by  decrease  of  volume.  Streams  flowing  through  arid 
regions  may  receive  Httle  water,  and  lose  much  by  evaporation  and 
by  soaking  into  the  dry  earth.  Many  streams  in  the  West  leave 
the  mountains  bank-full,  to  wither  and  disappear  on  the  lower  lands. 
Many  also  have  much  of  their  water  withdrawn  for  purposes  of 
irrigation.  (3)  Tributary  streams  with  high  gradients  may  bring 
to  the  main  streams  more  sediment  than  the  latter  can  carry  away. 


Fig.  151.    Alluvial  fan  at  the  mouth  of  Aztec  Gulch,  southwestern  Colorado. 
(U.  S.  Geol.  Surv.) 


(4)  Many   rivers    deposit  at  their  mouths,    where  the    current    is 
checked. 

Deposits  at  the  bases  of  steep  slopes.  Every  shower  washes 
fine  sediment  down  the  slopes  of  hills  and  mountains,  and  much  of 
it  is  left  at  their  bases,  where  the  velocity  of  the  water  is  checked 
suddenly.  At  the  lower  end  of  every  new-made  gully  on  a  hillside, 
there  is  a  mass  of  debris  which  was  washed  out  of  the  gully  itself 
(Fig.  127).  Material  in  such  positions  accumulates  in  the  form 
of  an  alluvial  cone,  or  a  gentler  sloping  alluvial  fan  (Fig.  151).  The 
rivers  descending  from  the  Sierras  to  the  valley  of  California  have 
built  great  fans  along  the  foot  of  the  range,  and  most  of  the  rivers 
coming  out  of  the  Rockies  to  the  plains  east  of  them  have  done  the 


236 


MODIFICATION  OF  LAND  SURFACES 


same  thing.  Many  of  the  fans  of  streams  descending  from  the  west- 
ern mountains  are  miles  across.  Fans  made  by  neighboring  streams 
may  grow  until  they  unite  to  form  a  compound  alluvial  Jan,  or  a  pied- 
mont alluvial  plain.  Such  plains  exist  at  the  bases  of  many  mountain 
ranges.     Their  alluvial  deposits  may  be  hundreds  of  feet  thick. 

Many  alluvial  fans  and  piedmont  alluvial  plains  are  valuable 
for  farming.     (In  general,  which  would  be  more  valuable,  the  higher 


Fig.  152.     Cultivated  alluvial  fan  near  Riverside,  California. 

or  the  lower  portions  of  alluvial  fans?  Why?)  In  parts  of  southern 
California,  for  example,  such  lands  are  so  valuable  that  farms  are 
very  small  and  highly  improved  (Fig.  152).  Water  is  supplied  (i) 
by  wells,  through  which  the  fan  is  made  to  yield  up  the  water  it  has 
absorbed,  or  (2)  by  irrigating  ditches  which  connect  with  a  stream 
or  reservoir  at  a- greater  height.  Many  villages  in  mountain  valleys 
are  situated  on  alluvial  fans.  The  agricultural  settlements  of  Utah 
spread  southward  from  the  vicinity  of  Great  Salt  Lake  along  the 
piedmont  alluvial  plain  at  the  west  base  of  the  Wasatch  Mountains. 
Most  of  the  cities  and  villages  of  the  state  are  within  this  belt. 

Deposits    in    valley   bottoms;    flood-plains    and    man.    The 
gradient  of  a  stream  generally  becomes  less  toward  its  mouth,  and 


FLOOD-PLAINS  AND  MAN 


237 


so  it  happens  that  sediment  is  spread  for  great  distances  along  valley 
bottoms.  Some  of  it  is  left  in  the  channels,  and  some  is  spread  over 
the  low  lands  along  the  streams,  making  alluvial  plains. 

Streams  sometimes  deposit  sand  bars  in  their  channels,  especially  in  low 
water.  Bars,  and  the  tree  trunks  and  snags  which  they  often  catch  and  hold, 
hinder  navigation,  especially  when  rivers  are  low.  In  earlier  years,  many  steam- 
boats were  wrecked  by  such  obstructions  in  the  Missouri  and  Mississippi  rivers. 
Later,  large  sums  of  money  were  spent  in  removing  snags  and  dredging  channels. 

Alluvial  plains  along  large  rivers  are  almost  flat,  though  they 
slope  gently  down-stream,  and  many  of  them  have  natural  levees. 
This  term  is  applied  to  the  low  ridges  along  the  banks  of  the  channel 
(Fig.  153).  In  times  of  flood,  the  current  in  the  main  channel  is 
swift;  but  so  soon  as 
the  water  spreads  be- 
yond its  channel,  its 
velocity  is  checked  be- 
cause its  depth  sud- 
denly becomes  less,  and 
it  promptly  abandons 
much  of  its  load.  Dur- 
ing the  period  of  over- 
flow, the  edges  of  the  channel  current  are  checked  by  the  slower 
moving  flood-plain  water,  and  this  causes  further  deposition  on  the 
banks  of  the  channel.  Repeated  deposition  in  this  position  gives  rise 
to  levees.  Embankments  have  been  built  by  man  upon  the  natural 
levees  of  some  rivers  to  prevent  the  flooding  of  the  valley  flats,  and  to 
permit  the  settlement  of  the  bottom  lands.  Louisiana  alone  has  spent 
more  than  $35,000,000  since  1865  in  levee  building,  and  is  expending 
now  about  $800,000  a  year  in  this  way.  (Why  must  the  protective 
levees  be  built  higher  and  higher  as  time  passes?)  In  spite  of  such 
improvements,  floods  are  unfortunately  frequent.  The  damage 
which  they  did  to  buildings,  bridges  (Figs.  154  and  155),  railroads, 
etc.,  in  the  United  States  in  1908  was  estimated  at  more  than  $237,- 
000,000,  though  not  all  this  damage  was  done  on  the  flood-plains  of 
large  rivers.  Impressive  as  this  estimate  is,  it  takes  no  account  of 
the  great  damage  done  to  the  land  itself,  nor  is  it  possible  to  measure 
the  suffering  and  reduced  efficiency  of  the  people  living  where  there 
have  been  great  floods. 

In  early  days,  most  of  the  people  in  Louisiana  and  Mississippi 
lived  in  narrow  belts  along  the  levees  of  the  Mississippi  and  its 


Fig.  153,     Diagram  showing  natural  levees. 


238 


MODIFICATION  OF  LAND   SURFACES 


Fig.   154.     Railway  bridge  over  the   Nolichucky  River  at  Unaka  Springs, 
Tennessee.     (From  photograph  by  Glenn,  U.  S.  Geol.  Surv.) 


Fig- 155-     Same  place  as  shown  in  Fig.  154  after  the  bridge  and  piers  were  swept 
away  by  the  flood  of  May,  igoi.     (From  photograph  by  Glenn.  U.  S.  Geol.  Surv.) 


TOWN  SITES  AND   RIVERS 


239 


Fig.  156.  The  Rio  Grande  near  Browns- 
ville, Texas. 


branches.  The  land  here  was  high  enough  and  dry  enough  to  be 
farmed,  very  fertile,  and  close  to  the  streams  which  were  the  great 
highways  of  that  time.  The  plantations  were  narrow  along  the 
streams,  and  extended  back,  at  right  angles  to  them,  until  the  land 
became  too  low  and  wet  to 
cultivate. 

A  stream  in  an  allu\dal  plain 
is  likely  to  wind  about,  or 
meafider  (Fig.  156).  This  is  the 
result  of  the  low  velocity  of 
such  a  stream,  for  sluggish 
streams  are  turned  aside  easily. 
Were  such  a  stream  made 
straight,  it  would  become 
crooked  again,  for  the  banks 
of  all  streams  are  less  firm  at  some  places  than  at  others,  and  the 
stream  would  cut  more  at  those  places.  Once  started,  meanders  tend 
to  become  more  and  more  pronounced  (Fig.  157)  until,  probably  in 
some  time  of  flood,  the  stream  cuts  through  the  neck  of  the  meander 
and  straightens  its  course.  When  a  stream  has  cut  off  a  meander, 
the  abandoned  part  of  the  channel  may  remain  for  a  time  unfilled 
with  sediment.  If  it  contains  standing  water,  it  becomes  the  site 
of  an  oxbow  lake  or  bayou  (Fig.  156). 

In  meandering,  a  stream  sometimes  reaches  and  undermines  the 
valley  bluff,  thus  widening  its  valley  flat.  This  is,  indeed,  the  most 
important  process  in  the  widening  of 
valley  flats  (p.  223).  Towns  grew  up 
early  on  the  bluft"s  of  the  lower  ISIissis- 
sippi  at  points  where  the  nvev  touched 
the  side  of  its  valley.  In  this  way  the 
location  of  Natchez,  Vicksburg,  IMem- 
phis,  and  other  places  was  determined. 
Such  sites,  overlooking  and  controlling 
the  river,  were  bones  of  contention 
between  Spain  and  the  United  States  during  the  dispute  over 
the  southwestern  boundary,  from  1783  to  1795.  The  same  physio- 
graphic features  located  the  Confederate  defenses  in  the  Civil  War 
at  Columbus  (Ky.),  Ft.  Pillow  (Tenn.),  Vicksburg  (Miss.),  Grand 
Gulf  (Miss.),  and  Port  Hudson  (La.). 

By  shifting  their  courses,  as  the  result  of  deposition  and  meander- 


Fig.  157.    Diagram  showing 
development  of  a  meander. 


240 


MODIFICATION  OF  LAND  SURFACES 


ing,  streams  have  afifected  human  interests  in  many  other  ways.  Vil- 
lages which  grew  up  on  the  banks  of  navigable  rivers  because  of 
the  river  trade,  in  some  cases  have  been  left  far  from  the  streams 
by  changes  in  the  positions  of  the  latter.  Such  villages  usually 
decline  when  the  streams  withdraw  their  patronage.  Other  places 
built  on  river  banks  have  been  preserved  at  great  expense,  while 
some  have  been  washed  away.  The  Mississippi  River  flows  over 
the  site  of  Kaskaskia,  one  of  the  most  important  French  settle- 


Fig.  158.     A  delta  in  a  lake  in  Switzerland.     (From  photograph  by  Robin.) 


ments  in  the  upper  Mississippi  Valley,  and  the  first  capital  of 
Illinois.  The  Missouri  River  destroyed  Franklin,  Missouri,  an 
outfitting  place  in  the  1820 's  for  the  trade  across  the  Great  Plains 
to  Santa  Fe. 

Many  streams  have  been  used  as  boundaries  between  counties  and  states. 
In  numerous  cases  the  shifting  of  the  stream  has  led  to  boundary  disputes,  for,  by 
the  cutting  off  of  meanders,  tracts  of  land  have  been  shifted  from  one  state  to 
another.  In  the  case  of  the  Missouri  River,  there  have  been  disputes  between 
Nebraska  and  South  Dakota,  Nebraska  and  Iowa,  and  Nebraska  and  Missouri. 
The  Supreme  Court  finally  decided  that  when  the  Missouri  develops  a  cut-off,  the 
boundary  line  does  not  shift  with  the  river,  but  remains  where  it  was.  Again, 
many  boundaries  have  been  defined  as  following  the  "main  channels"  of  streams. 
Where  there  are  several  channels,  which  is  the  case  in  many  rivers,  the  question  may 
arise  as  to  which  one  is  the  main  channel.  Furthermore,  the  main  channel  at  one 
time  may  be  a  subordinate  channel  at  another  time.  These  conditions  have  led  to 
disputes  over  the  ownership  of  islands  in  different  rivers. 

The  objections  to  rivers  as  boundaries  are  most  serious  where  they  form  inter- 
national boundaries.  Thus  the  shifting  of  the  Rio  Grande  makes  it  a  poor  bound- 
ary between  the  United  States  and  Mexico.  In  addition,  so  much  water  was  taken 
from  the  Rio  Grande  for  irrigation  in  southern  Colorado  and  New  Mexico  that 
there  was  little  water  for  Mexican  farmers  below  El  Paso.  Mexico  protested  to 
the  United  States,  and  finally  it  was  arranged  that  the  United  States  should  build 


DELTAS  AND  THEIR  RELATIONS  TO  MAN        241 

a  great  reservoir  on  the  Rio  Grande  north  of  EI  Paso,  to  store  the  water  of  the  river, 
and  that  Mexico  should  receive  a  certain  fixed  amount  of  water  from  this  reservoir 
each  year. 

Most  flood-plains  are  very  fertile,  but  many  are  too  wet  to  be 
cultivated  without  drainage.  About  one-sixth  of  Arkansas,  for  ex- 
ample, is  swampy,  but  most  of  its  swamp  area  is  rich  alluvial  land. 
When  drained,  the  wet  lands  of  the  United  States  will  form  one  of  ^he 
greatest  resources  of  the  nation  (p.  300). 

Deltas  and  their  relations  to  man.  Where  a  stream  flows 
into  the  sea,  or  into  a  lake,  its  current  is  checked  promptly,  and 


Fig.  159.     The  lower  part  of  the  delta  of  the  Mississippi  River. 

soon  stopped  entirely.  Its  load  therefore  is  dropped,  and  if  not 
washed  away  by  waves  and  currents,  makes  a  delta  (Fig.  158).  That 
part  of  a  delta  above  the  surface  of  the  water  in  which  it  is  built 
is  like  a  nearly  flat  alluvial  fan.  Deltas  may  be  built  where  one  stream 
flows  into  another,  especially  where  a  swift  stream  with  much  sedi- 
ment joins  a  slow  one. 

Much  land  has  been  made  by  the  growth  of  deltas.  Thus  the 
Colorado  River  has  built  a  great  delta  across  the  Gulf  of  California 
near  its  former  upper  end.  In  the  arid  climate  of  the  region,  the  shut- 
off  head  became  a  nearly  dry  basin,  the  lowest  part  of  which  is  about 
300  feet  below  sea-level.    The  soil  being  good,  water  alone  was  needed 


242 


MODIFICATION  OF  LAND   SURFACES 


Fig.  i6o.  Delta  of  the  Nile 
River.  The  dotted  area  is 
desert. 


to  make  this  area  fertile,  and  the  results  that  have  followed  the 
irrigation  of  parts  of  it  justify  its  new  name,  the  "Imperial  Valley." 
Figs,  dates,  and  other  tropical  products  grow  here  luxuriantly.  The 
deltas  of  the  Mississippi  (Fig.  159),  the  Nile  (Fig.  160),  and  the 

Hwang-ho  (Fig.  161)  rivers  are  among 
the  large  and  well-known  ones.  The 
delta  of  the  Ganges  and  Brahmaputra 
has  an  area  (above  water)  of  some 
50,000  square  miles  (nearly  as  large  as 
Illinois). 

While  rivers  have  made  much  delta 
land,  it  is  to  be  remembered  that  the 
material  of  which  they  are  composed  has 
been  removed  from  vastly  larger  areas, 
and  that  much  of  it  was  rich  soil.  It  is 
probable  that  the  loss  to  man  through 
the  removal  of  such  material  is  far  greater  than  the  gain  resulting 
from  its  deposition. 

The  surfaces  of  most  deltas  are  nearly  flat,  and  the  streams  which  cross  them 
often  give  off  branches,  called  distributaries,  which  flow  independently  to  the  edge 
of  the  delta,  and  are  subject  to  frequent  changes.     These  changes  sometimes  affect 

commerce  in  a  vital  way  (p.  351). 
The  distributaries  of  the  Mississippi 
offered  the  English  in  the  War  of  181 2, 
and  the  Federals  in  1862,  several  pos- 
sible lines  of  approach  to  the  vicinity 
of  New  Orleans.  The  necessity  of 
watching  these  different  lines  scat- 
tered the  men  and  the  resources,  and 
weakened  the  resistance  of  the  de- 
fenders of  the  city.  By  cutting  the 
levees  and  flooding  the  lower  land, 
General  Jackson  was  able  to  increase 
greatly  the  diflSculties  of  the  English. 

Most  delta  land  away  from 
natural  levees  is  low  and  wet, 
and  must  be  diked  and  drained 
before  it  can  be  farmed.  The  soil  of  great  deltas  is  deep  (What 
determines  its  thickness?),  and  in  most  cases  rich  in  the  mineral 
elements  of  plant  food.  Some  deltas,  like  that  of  the  Hwang-ho, 
support  dense  populations.  Delta  lands  are,  however,  subject  to 
disastrous  floods.     It  is  estimated  that  the  flood  of  the  Hwang-ho 


Fig.  161.     Delta  of  the  Hwang-ho. 


ALLUVIAL  TERRACES  243 

River  in  September,  1887,  drowned  more  than  a  million  people  and 
caused  the  death  of  many  more  by  disease  and  famine  afterward. 

Previous  to  1853,  the  Hwang-ho  had  flowed  for  many  years  into  the  Yellow 
Sea  south  of  the  Shan-tung  promontory  (Fig.  161).  In  that  year,  it  shifted  its  course 
in  flood  time,  forming  a  new  channel  leading  northeast  into  the  Gulf  of  Pechih,  300 
miles  north  of  its  former  mouth.  Other  changes  at  earlier  times,  running  as  far 
back  as  2293  b.  c,  are  recorded  in  the  annals  of  Chinese  history. 

Lakes  exist  on  many  large  deltas.  Some  are  former  sections  of  the 
shifting  streams,  and  some  (Fig.  159)  are  portions  of  the  sea  or  lake 
in  which  the  delta  is  built,  portions  that  were  surrounded  by  the 
deposits  or  shut  in  between  them  and  the  former  shore-line. 

Delta  cities  have  peculiar  problems,  as  illustrated  by  New  Orleans.  For  a 
long  time,  floods  were  of  almost  yearly  occurrence.  In  1849,  for  example,  220  in- 
habited squares  were  flooded  and  12,000  people  were  driven  from  their  homes. 
Street  improvement  was  difficult;  there  were  no  paving  stones  save  those  brought 
as  ballast  in  ships.  As  late  as  1835,  only  two  streets  were  paved  for  any  consider- 
able distance.  On  the  other  streets,  carriages  in  wet  weather  sank  to  the  axle  in 
mire.  The  question  of  a  domestic  water  supply  was  an  early  and  pressing  one, 
and  for  a  long  time  the  practice  was  general  of  building  cisterns  to  catch  the  rain- 
water. The  city  could  not  easily  empty  its  sewage  into  the  Mississippi,  for  the 
banks  of  the  river  are  above  the  houses.  Under  these  conditions,  the  city  was 
for  years  a  very  unhealthful  place.  In  recent  years  these  disadvantages  have 
been  largely  overcome.  New  Orleans  now  pumps  its  sewage  into  the  river, 
cisterns  are  condemned,  many  streets  are  well  paved,  and  the  city  is  much  more 
healthful  than  formerly. 

Alluvial  terraces.  When  a  river  which  has  an  alluvial  flat  is  reju- 
venated (p.  233),  the  stream  sinks  its  channel  below  the  level  of  the  flat. 
The  remnants  of  the  old  flood-plain  are  then  alluvial  terraces  (Fig.  162). 
Such  terraces  are  also  formed  in  other  ways.  Thus  if  a  stream  is  sup- 
plied for  a  time  with  an  excess  of  load,  it  aggrades  (builds  up)  its  valley. 
If,  later,  the  excess  of  sediment  ceases,  the  stream  sets  to  work  to  re- 
move that  which  was  temporarily  laid  aside  in  its  flood-plain. 

The  material  of  many  alluvial  terraces  is  gravelly  or  sandy, 
and  their  soils  vary  greatly  in  value.  Many  towns  and  cities  are 
built  on  alluvial  terraces.  (What  advantages  would  such  locations 
have  over  sites  on  flood-plains?  On  the  edges  of  valley  bluffs?) 
The  leading  towns  of  the  Platte  Valley  in  Nebraska  are  on  terraces 
near  the  mouths  of  tributary  valleys.  (Of  what  significance  is  the 
last  fact?)  In  the  middle  Illinois  Valley,  every  town  is  on  a  terrace, 
and  every  terrace  has  a  town.  Terrace  sites  were  chosen  for  most  of 
the  first  settlements  of  the  Connecticut  Valley,  such  as  Hartford, 
Weathersfield,  and  Windsor. 


244 


MODIFICATION  OF  LAND  SURFACES 


Summary.     From  the  physiographic  standpoint,  the  mission  of 
running  water  is  to  wear  the  land  to  base-level.     The  material  it 


Fig.  162.     Terrace  of  the  Columbia  River.     (Willis.) 

carries  toward  and  to  the  sea  is  prepared  for  transportation  largely  by 
the  agents  of  weathering,  and  in  subordinate  amount  is  worn  from  the 
solid  rocks  by  the  streams  themselves.     The  irregular  wearing  down 


A 

'^^ 

'■^.. 

^ 

>- 

1        1 

-/'*' 

1 

Figs.  163,  164.     Drainage  maps  of  contrasted  areas  of  equal  size. 

of  the  land  produces  most  of  the  familiar  relief  features  of  the  surface. 
Their  characteristics  are  determined  by  several  factors,  especially 


QUESTIONS 


245 


by  the  character  and  position  of  the  rocks  from  which  they  were 
carved,  and  the  stage  of  development  which  they  have  reached.  On 
its  way  to  the  sea,  the  waste  of  the  land  is  often  laid  aside  by  over- 
loaded streams,  forming  topographic  features  subject  to  later  destruc- 
tion by  eroding  waters  or  by  other  agencies.  All  phases  of  river  work 
affect  human  interests  vitally.  Much  can  be  done  by  regulating  and 
controlling  streams  to  increase 
their  usefulness  and  prevent 
their  doing  damage. 


QUESTIONS 

1.  In  what  parts  of  the  United 
States  would  a  valley  need  to  be  deep 
to  have  a  permanent  stream? 

2.  What  are  all  the  conditions 
which  may  help  to  make  the  flow  of 
streams  (i)  regular,  and  (2)  irregular? 

3.  Why  do  streams  carry  more 
and  coarser  material  during  floods 
than  at  other  times? 

4.  Is  the  bed  of  the  upper  St. 
Lawrence  River  being  eroded  much? 
Why? 

5.  (i)  Why  is  the  rate  of  erosion 
in  the  Colorado  Basin  so  rapid  (Fig. 
126),  especially  in  view  of  the  fact 
that  a  large  part  of  it  is  in  an  arid 
region?  (2)  Why  is  the  rate  in  the 
basin  of  the  Red  River  of  the  North 
relatively  so  slow  (Fig.  126)? 

6.  Why  are  steep  slopes  charac- 
teristic of  arid  climates? 

7.  What  is  the  age,  in  terms  of 
erosion,  of  the  area  shown  in  Fig.  80? 

8.  (i)  Interpret   the   contrasted  Fig.  165. 
drainage  shown  by  Figs.  163  and  164. 

(2)  In  what  stage  of  erosion  is  the  area  shown  by  Fig.  163?     (3)  Does  Fig.  164 
indicate  the  stage  of  erosion  which  that  area  has  reached?     Why? 

9.  (i)  What  topographic  features  are  shown  in  Fig.  165?  (2)  Compare 
and  contrast  the  northern  and  southern  parts  of  the  area  as  to  (a)  the  climate, 
(b)  the  character  of  the  rocks,  and  (c)  the  work  of  the  streams. 

10.  In  general,  what  stream-built  features  are  (i)  most,  and  (2)  least  endur- 
ing?    Why? 

11.  State  all  the  important  ways  in  which  (i)  stream  erosion  and  (2)  stream 
deposition  affect  human  interests. 


246  MODIFICATION  OF  LAND   SURFACES 

The  Work  of  Ice 

Snow  is  perhaps  the  most  common  form  of  ice,  but  ice  on  pondsj 
lakes,  and  rivers  is  familiar  to  all  who  live  where  winters  are  cold. 
In  middle  latitudes  the  water  in  the  soil  and  rocks  freezes  in  winter, 
often  to  a  depth  of  several  feet.  In  some  parts  of  the  world,  too,  there 
are  glaciers.  In  most  of  its  forms  ice  has  some  effect  on  the  surface 
of  the  land. 

Ice  on  lakes  and  rivers.  Most  lakes  and  rivers  in  middle  lati- 
tudes are  frozen  over  for  several  months  each  year.  This  is  in  some 
cases  a  great  disadvantage  from  the  standpoint  of  commerce.  The 
upper  Mississippi  River  is  closed  to  navigation  for  more  than  four 
months  of  the  year.  The  open  season  on  the  upper  Great  Lakes  lasts 
about  seven  months.  The  St.  Lawrence  River  is  closed  by  ice  about 
five  months  each  year,  and  is  difficult  to  enter  during  another  month. 
Hudson  Bay  and  its  tributary  rivers  are  closed  even  longer.  It 
was  a  great  disadvantage  to  the  French  colonies  of  interior  Canada  ■ 
that  they  were  shut  off  completely  from  the  mother  country  for 
nearly  half  the  year,  and  it  is  a  serious  disadvantage  to  Canada  to- 
day that  her  two  main  gateways  from  the  Atlantic  Ocean  are  closed 
so  much  of  the  time.  The  inland  waterways  of  England  and  France 
are  open  throughout  normal  years;  those  of  Germany  and  central 
Russia  are  closed  more  often,  and  for  longer  periods  the  farther  they 
are  from  the  Atlantic.  Those  of  northern  Russia  are  closed  for  five 
or  six  months.  (Why  are  the  waterways  of  western  Europe  so  in 
contrast  with  those  of  North  America  in  corresponding  latitudes?) 

In  some  cases,  the  ice  of  rivers  and  lakes  serves  a  good  purpose. 
Fishing  villages  formerly  were  built  on  the  ice  in  such  places  as  Sagi- 
naw Bay,  Michigan,  and  are  still  common  in  the  gulfs  of  Bothnia  and 
Finland.  When  frozen  over,  many  northern  rivers  serve  as  roadways 
for  local  business.  The  cutting  and  packing  of  ice  for  sale  during 
the  following  summer  is  an  important  industry  on  many  lakes  and 
rivers  in  northern  United  States. 

Ice  on  the  sea.  In  high  latitudes  ice  forms  on  the  sea  where 
the  w^ater  is  shallow,  and  in  polar  regions  it  becomes  several  feet 
deep,  even  on  the  open  sea.  Sea-ice  is  broken  up  in  the  summer, 
and  the  floating  pieces  are  c&Wed  floe-ice.  When  the  floes  are  crowded 
together,  they  make  ice-packs,  some  of  which  are  hundreds  of  miles 
across.  Ice-packs  are  obstacles  to  polar  navigation,  and  make  most 
of  the  north  coast  of  Russia  and  Siberia  useless  even  in  summer. 


FORMATION   OF   GLACIERS 


247 


The  closing  of  ocean  harbors  and  of  seas  connected  with  the 
ocean,  like  the  closing  of  inland  waters,  is  a  great  hindrance  to  com- 
merce. The  North  Sea  has  a  tremendous  advantage  over  the  Baltic 
in  this  regard.  The  shores  of  the  latter  are  hampered  by  ice  each 
winter,  while  those  of  the  former  are  edged  with  ice  only  during  the 
most  severe  weather.  The  key  to  Russian  expansion  since  the  days 
of  Peter  the  Great  has  been  the  attempt  to  secure  ice-free  harbors. 

EXISTING  GLACIERS 

General 
Conditions  for  glaciers.     Where  it  is  so  cold  that  snow  lasts  from 
year  to  year  over  any  considerable  area,  the  snow  constitutes  a  snow- 
field  (Fig.  1 66) .     Snow-fields  occur  in  mountains  in  nearly  all  latitudes, 
and  in  polar  regions  even  down  to  sea-level.     Where  snow  accumulates 


Fig.  166.     Snow-fields  in  Alaska.     Russell  Fiord  at  right  of  view.    (Brabazon, 
Canadian  Boundary  Commission.) 

to  great  depths  and  lies  long  on  the  surface,  it  changes  to  compact 
ice,  and  becomes  an  ice-field.  The  beginning  of  this  change  is  distinct 
in  banks  of  snow  which  last  for  some  weeks.  Such  banks  are  made  up  of 
coarse  granules  of  ice,  sometimes  as  large  as  peas.  The  change  from 
flakes  of  snow  to  granules  of  ice  is  due,  in  part,  to  the  melting  of  the 
snow  and  the  re-freezing  of  the  water.  If  there  is  much  snow,  it  is 
compressed  by  its  own  weight,  and  after  being  compacted  in  this  way, 
the  freezing  of  the  sinking  water  binds  the  granules  together.  When 
the  amount  of  ice  made  from  snow  becomes  great  enough,  it  moves 
out  slowly  from  the  place  where  it  was  formed  to  lower  and  warmer 
places.     When  it  begins  to  move,  it  becomes  a  glacier. 


248 


MODIFICATION  OF  LAND   SURFACES 


Functions  of  glaciers,  (i)  One  mission  of  glaciers  is  to  return  to 
lower  and  warmer  levels  moisture  which  otherwise  would  be  locked  up 
indefinitely  as  snow  and  ice.     (2)  Like  rivers,  glaciers  wear  the  land 

(3)  Long  after  glaciers 


and  move  the  resulting  waste  toward  the  sea 


ft 

fem^ 

1% ::  jgHH 

B 

1  ' '  ;^  jH^^^^^^^^H 

[  -t^M 

1^1 

H 

^R 

i^B 

^H 

ll&^'  .,>^iM^HH^^^^I 

^Hi 

Fig.  167.     A  valley  glacier  in  the  Cascade  Mountains,  Washington.     (Willis, 
U.  S.  Geol.  Surv.) 


have  melted  away,  some  of  their  effects  on  the  conditions  of  life  remain, 
because  of  the  changes  they  made  in  topography,  soil,  and  drainage. 
Thus  past  glaciation  is  a  leading  factor  in  the  geography  of  northern 
United  States  and  northern  Europe.  (4)  Glaciers  tend  to  maintain  a 
relatively  uniform  volume  in  the  streams  which  flow  from  them,  and  in 
various  mountain  regions  such  streams  afford  great  amounts  of  power. 


TYPES  OF  GLACIERS 


249 


Tj^es  of  glaciers.  Glaciers  have  various  forms,  depending 
on  the  amount  of  ice  and  on  the  shape  of  the  surface  beneath  and 
around  them.  If  the  snow-field  which  gives  rise  to  a  glacier  is 
at  the  upper  end  of  a  mountain  valley,  the  ice  moves  down  the  valley 
as  a  valley  glacier  (Fig.  167).  In  high  latitudes,  snow-fields  and 
ice-fields  may  lie  on  plains  or  plateaus.  When  the  ice  in  such  situ- 
ations begins  to  spread,  it 
moves  in  all  directions  from  its 
center.  Such  glaciers  are  ice- 
caps or  ice-sheets.  Very  large 
ice-caps  sometimes  are  called 
continental  glaciers.  The  main 
ice-caps  of  Antarctica  and 
Greenland  (Fig.  16S)  are  large, 
but  small  ones  are  found  on 
various  promontories  along  the 
coast  of  Greenland,  on  Iceland, 
and  on  some  other  Arctic  islands. 
Glaciers  occur  also  at  the  bases 
of  some  mountains,  being 
formed  by  the  union  of  the 
spreading  ends  of  valley  gla- 
ciers. Such  glaciers  are  pied- 
mont glaciers.  Of  these  types, 
valley  glaciers  are  most  com- 
mon and  most  familiar,  but  the 
large  ice-caps  contain  much 
more  ice. 


Fig.  168.     Map  of  Greenland  ice-cap. 


Valley  Glaciers 
Distribution.  The  chief  re- 
gions of  valley  glaciers  are  the 
high  mountains  of  Eurasia,  the  southern  Andes,  and  the  higher  moun- 
tains of  northwestern  United  States  and  western  Canada.  In  Alaska, 
high  mountains  near  the  coast  receive  abundant  precipitation  from 
the  ocean  winds.  The  heavy  snowfall  on  the  upper  slopes  feeds  many 
glaciers,  some  of  which  reach  the  sea. 

The  glaciers  of  Switzerland  are  known  best  and  help  to  attract  thousands  of 
tourists  to  that  country  each  year.  In  1910,  Congress  created  Glacier  National 
Park  on  the  Continental  Divide  in  northwestern  Montana  (Fig.  224}.     It  is  about 


25C  MODIFICATION  OF  LAND   SURFACES 

sixty  miles  in  length  and  contains  more  than  sixty  glaciers.  This  may  become  one 
of  the  best  known  and  most  visited  of  our  National  Parks,  for  the  mountains  ani 
glaciers  offer  the  chance  for  mountaineering  of  real  Alpine  character,  the  streams 
abound  in  trout,  and  the  mountains  still  shelter  enough  game  animals  to  become 
an  important  game  refuge.  The  park  contains  one  of  the  most  beautiful  portions 
of  the  Rocky  Mountains  lying  within  the  United  States. 

Size.  There  are  nearly  2,000  glaciers  in  the  Alps,  only  one 
of  which  has  a  length  of  ten  miles.  Less  than  40  have  a  length 
of  five  miles,  while  the  great  majority  are  less  than  one  mile  long. 
Only  a  few  are  so  much  as  a  mile  wide,  and  none  are  more  than  a 
few  hundred  feet  thick.  Larger  glaciers  occur  in  the  Caucasus 
Mountains  and  in  Alaska.  Seward  Glacier  in  Alaska  is  more  than 
50  miles  long,  and  is  three  miles  wide  at  the  narrowest  place.  The 
glaciers  of  western  United  States  south  of  Alaska  are  not  so  large 
as  the  larger  glaciers  of  the  Alps. 

Movement.  The  ice  of  a  glacier  is  wasting  all  the  time,  both 
by  melting  and  evaporation.  In  spite  of  this,  many  glaciers  remain 
about  the  same  size  year  after  year.  This  is  because  the  loss  by 
melting  is  replaced  by  advance  from  the  snow-fields,  from  which  the 
ice  creeps  down  the  valleys  until  it  reaches  a  place  so  warm  that  the 
melting  at  the  end  balances  the  forward  motion.  Most  glaciers  move 
very  slowly.  Of  those  whose  rate  of  advance  has  been  measured, 
few  move  more  than  two  feet  a  day,  and  very  few  as  much  as  seven. 

The  rate  of  movement  depends  chiefly  on  (i)  the  thickness  of  the  moving  ice, 
(2)  the  slope  of  the  surface  over  which  it  moves,  (3)  the  slope  of  the  upper  surface 
of  the  ice,  and  (4)  the  topography  of  its  bed.  (What  combination  of  conditions 
would  favor  most  rapid  movement?)  The  exact  nature  of  glacier  movement  is  a 
disputed  question.  It  was  thought  formerly  that  glaciers  flowed  somewhat  as 
stiff  liquids  do,  but  it  is  very  doubtful  if  the  motion  is  really  flowage. 

Ice-Caps 

As  already  stated,  ice-caps  may  lie  on  plains  or  plateaus,  and 
may  be  large  or  small. 

Greenland  has  an  area  of  400,000  to  600,000  square  miles,  and  all  but 
its  borders  is  buried  beneath  one  vast  field  of  ice  and  snow  (Fig.  168). 
Except  on  a  narrow  border  of  a  mile  or  so  at  the  edge  of  the  ice-sheet, 
not  even  a  bowlder  or  a  pebble  interrupts  the  great  expanse  of  white. 

The  thickness  of  the  Greenland  ice  is  not  known,  but,  where 
thickest,  it  is  probably  thousands  of  feet.  Near  its  margin  the 
ice  is  much  crevassed,  but  the  interior  is  fairly  smooth  so  far  as  known. 
The  ice  of  this  great  field  is  creeping  slowly  outward      The  rate  of 


THE  POLAR  ICE-CAPS 


251 


Fig.  169.     An  iceberg. 


movement  never  has  been  measured,  and  is  probably  not  the  same 
at  all  points,  but  it  has  been  estimated  not  to  exceed  a  foot  a  week. 
This  ice-cap  is,  in  one  sense,  more  of  a  desert  than  the  Sahara,  since 
it  is  inhabited  even  less  than  the  latter. 

Where  the  edge  of  the  Greenland  ice-cap  lies  a  few  miles  back  from 
the  coast,  the  rock  plateau  outside  it  has  many  valleys  leading  down 
to  the  sea.  Where  the  edge  of  the  ice-cap  reaches  the  heads  of  these 
valleys,  ice  moves  down  them, 
making  valley  glaciers.  Many 
of  the  latter  reach  the  sea, 
where  their  ends  are  broken  off 
and  float  away  as  icebergs. 
This  is  the  source  of  most  of 
the  bergs  (Fig.  169)  seen  from 
steamers  which  cross  the  North 
Atlantic.  Some  are  so  large 
that  they  float  far  to  the  south  before  they  are  melted.  Since  they 
are  sometimes  surrounded  by  fog,  they  are  a  menace  to  ships  (p.  149). 

The  Antarctic  snow-and-ice-cap  is  much  larger  than  that  of 
Greenland,  but  its  area  is  not  so  well  known.  It  is  probably  several 
million  square  miles  in  extent,  and  the  thickness'  of  its  ice  probably 
exceeds  that  of  Greenland.  The  ice  descends  to  the  sea  at  many 
points,  and  huge  blocks  of  it  become  icebergs. 

Piedmont  Glaciers 
A  number  of  alpine  glaciers  come  down  adjacent  valleys  in  the 
St.  Elias  range  of  Alaska,  and  spread  out  on  a  low  plain  at  its  base. 
So  much  do  their  ends  spread  that  they  unite  to  form  a  single  body 
of  ice,  70  miles  long  and  20  to  25  miles  wide,  called  the  Malaspina 
Glacier.  Its  area  is  greater  than  that  of  Delaware.  Its  central 
portion  is  free  from  debris,  but  has  thousands  of  deep,  wide  cracks. 
A  belt  along  the  margin  of  the  glacier  five  miles  or  less  in  width  is 
covered  by  rocky  and  earthy  debris,  and  parts  of  it  are  clothed  with 
vegetation.  The  undergrowth  is  here  so  thick  that  travelers  have  to 
cut  paths,  and  on  the  edge  of  the  ice  there  are  trees  three  feet  in  diam- 
eter.    Other  glaciers  of  the  same  type  occur  about  North  Greenland. 


ANCIENT  GLACIERS 

There  have  been  times  when  glaciers  were  much  more  extensive 
than  now,  for  various  features  produced  only  by  glaciation  (pp.  255- 


252 


MODIFICATION  OF  LAND  SURFACES 


265)  are  found  in  many  places  now  free  from  ice.  The  latest  of  these 
periods  is  known  as  the  Glacial  Period.  In  this  country,  glaciers 
existed  even  in  the  mountains  of  New  Mexico,  Arizona,  and  Nevada. 


Fig.  170.     Sketch-map  showing  the  area  in  North  America  covered  by  ice  at 
the  stage  of  maximum  glaciation.     (Chamberlin.) 


The  amount  of  ice  in  the  glaciers  of  Utah  or  Colorado  was  then 
far  greater  than  all  that  now  exists  in  the  United  States  south  of 
Alaska.  At  the  same  time,  a  great  area  east  of  the  Cordilleran 
mountain  system,  some  4,000,000  square  miles  in  extent  (Fig.  170), 


THE  GLACIAL  PERIOD  253 

and  lying  partly  in  Canada  and  partly  in  the  United  States,  was 
covered  with  an  ice-sheet. 

The  ice-sheet  of  North  America  originated  in  two  principal  cen- 
ters, one  on  either  side  of  Hudson  Bay.  The  beginning  of  each  was 
doubtless  a  great  snow-field.  At  first  these  snow-  and  ice-fields  grew 
by  the  addition  of  snow,  and  later  also  by  the  spread  of  the  ice  to 
which  the  snow  gave  rise.  The  two  ice-sheets  finally  became  one 
by  growing  together.  This  great  continental  glacier  did  not  origi- 
nate in  mountains,  but  on  high  plains. 

When  largest,  the  ice-sheet  had  the  extent  shown  in  Fig.  170,  but 
there  was  an  area  of  8,000  to  10,000  square  miles,  mainly  in  south- 
western Wisconsin,  over  which  the  ice  did  not  spread.  This  is  known 
as  the  driftless  area,  because  there  are  no  ice  deposits  {drift)  in  it. 
In  the  Cordilleran  mountains  there  was  also  a  great  body  of  ice 
that  remained  somewhat  distinct  from  the  one  which  spread  from 
the  other  centers. 

There  was  extensive  glaciation  in  Europe  at  about  the  same  time. 
The  glaciers  of  the  Alps  were  then  many  times  as  large  as  those  of 
to-day.  On  the  south  they  extended  quite  beyond  the  mountain 
valleys,  and  spread  out  on  the  plains  of  northern  Italy,  where  they 
left  their  deposits.  Similar  conditions  existed  in  the  other  mountains 
of  Europe  where  glaciers  now  exist,  and  in  some  where  they  do  not. 
There  was  also  a  large  ice-sheet  in  northwestern  Europe,  but  its  area 
was  only  about  half  that  of  the  ice-sheet  of  North  America.  The 
principal  center  from  which  the  ice  spread  was  the  mountains  of 
Scandinavia. 

Great  ice-sheets  are  not  known  to  have  developed  in  other  con- 
tinents during  the  Glacial  Period,  but  their  valley  glaciers  were 
very  large. 

The  history  of  the  Glacial  Period  was  not  simple.  After  the  growth  of  the  first 
great  North  American  ice-sheet,  it  shrank  to  small  size,  or  disappeared  altogether. 
Then  followed  a  relatively  warm  period,  when  plants  and  animals  lived  in  the 
region  where  the  ice  had  been.  Another  continental  ice-sheet  then  spread  over  the 
region  from  which  the  first  had  melted,  and  extended  still  farther  south.  As  it 
advanced,  the  second  ice-sheet  in  places  buried  the  soil  which  had  formed  on  the 
drift  left  by  the  ice  of  the  first  epoch.  Such  soils,  here  and  there  containing  the  remains 
of  plants  which  grew  in  them,  are  one  means  by  which  it  is  known  that  there  was 
more  than  one  ice-sheet.  A  third,  fourth,  and  fifth  ice-sheet,  each  somewhat  smaller 
than  its  predecessor,  came  and  then  melted.  In  other  words,  there  were  several 
epochs  when  ice-sheets  were  extensive,  separated  by  epochs  when  they  were  much 
smaller,  or  when  they  had  disappeared  altogether.  The  ice-sheets  of  Europe  had  a 
similar  history. 


254 


MODIFICATION  OF  LAND   SURFACES 


Cause  of  glacial  epochs.  The  development  of  the  great  ice- 
sheets  was  due  to  a  change  in  climate,  and  especially  to  a  reduc- 
tion of  temperature.  The  cause  of  the  cold  is  not  known,  though 
many  explanations  have  been  suggested.  The  explanation  which 
seems  most  acceptable  is  that  the  change  of  climate  was  due  to  a 


Fig.  171.     Glaciated  surface  of  limestone.    The  view  shows  also  the  relation 
of  drift  to  the  bed-rock  beneath.     Kelleys  Island,  Ohio.     (Stauffer.) 


change  in  the  constitution  of  the  atmosphere.  An  increase  in  the 
amounts  of  carbon  dioxide  and  water  vapor  would  make  the  climate 
warmer  (pp.  31,  178),  while  any  great  decrease  in  these  things  would 
make  the  climate  much  colder.  Good  reasons  have  been  suggested 
for  variations  in  the  amounts  of  these  substances  in  the  air,  and 
also  for  the  heavy  snowfall  in  the  regions  where  the  ice-sheets 
existed.  Heavy  snowfall  is  quite  as  necessary  as  low  temper- 
ature for  extensive  glaciation. 


LAND   FORMS  DUE  TO  GLACIAL  EROSION        255 

CHANGES  DUE  TO  GLACIAL  EROSION 

How  glaciers  erode.  Clean  ice,  moving  over  smooth,  solid 
rock,  would  erode  little,  but  ice  carrying  pieces  of  rock  in  its  bottom 
wears  the  surface,  even  when  the  latter  is  smooth  and  solid.  Like 
wind  and  water,  therefore,  ice  erodes  by  means  of  the  rock  tools  which 
it  carries.  Each  kind  of  tool  does  its  appropriate  work.  Fine, 
earthy  material  in  the  bottom  of  the  ice  polishes  the  rock  below,  while 
sand  and  small  pebbles  make  scratches  (strm)  upon  it.  Grooves  are 
made  by  bowlders  held  in  the  bottom  of  the  ice  and  forced  along  under 


Fig.  172.     Glacial  trough  in  San  Juan  Mountains,  Colorado. 

great  pressure.  Meanwhile  the  tools  are  themselves  polished, 
scratched,  and  worn  smaller.  The  finest  products  of  the  grinding 
have  been  called  rock  flour.  Polished  and  striated  bed-rock  surfaces 
(Fig.  171)  are  among  the  clearest  marks  of  the  former  existence  of 
glaciers  in  many  places  now  free  from  ice. 

Changes  in  valleys.  Mountain  valleys  through  which  glaciers 
pass  are  widened  and  deepened,  and  their  walls  made  smoother 
(Figs.  172  and  173).  In  many  cases  the  heads  of  glaciated  valleys  are 
big,  blunt,  and  steep-sided.  Most  of  the  lakes  which  add  so  much  to 
mountain  scenery  are  (i)  in  rock  basins  gouged  out  of  valley  floors 
by  glaciers  (Fig.  173),  or  (2)  behind  dams  formed  by  the  deposits 
of  the  ice  (Fig.  186).  Tributary  valleys  commonly  join  their  main 
valleys  at  the  level  of  the  latter,  but  the  bottoms  of  many  valleys 
that  were  deepened  and  widened  by  former  glaciers  are  much  (in 
some  cases  500  to  1,000  feet)  lower  than  the  lower  ends  of  their  tribu- 
taries. In  such  cases  streams  descend  in  rapids  or  falls  from  the 
tributary  hanging  valleys  (Fig.  174).     Much  water  power  is  afforded 


256 


MODIFICATION  OF  LAND  SURFACES 


by  such  rapids  and  falls  in  the  mountains  of  western  United  States, 
Switzerland,  and  northwestern  Europe. 

The  ancient  ice-sheet  overrode  hills  and  divides  as  well  as  valleys. 
In  many  cases  the  ice  deepened  the  valleys  more  than  it  lowered 
the  hills,  and  where  this  was  true  it  increased  the  relief,  even  though 
it  reduced  the  roughness  of  the  surface. 

Elevations  reduced  and  changed  in  shape.  Hills  overridden 
by  ice-sheets  are  worn  down  and  smoothed  off,  and  the  wear  is 


n.-" 


A^ 


Fig.  173.  A  valley  in  the  Needle  Mountains,  Colorado,  cleared  of  all  earth 
and  loose  rock  by  a  glacier  which  once  passed  through  it.  The  moving  ice  also 
smoothed  all  the  projecting  points  of  rock. 

greatest  on  the  side  of  the  hill  against  which  the  ice  moves  (Fig. 
175).  Many  small  elevations  were  worn  away  entirely  by  the  con- 
<:inental  glaciers. 

Ice-shaped  coasts.  Glaciers  which  descend  into  the  sea  through 
hays  tend  to  gouge  out  the  bay-bottoms,  and  to  wear  back  the  bay- 
heads.  If  such  glaciers  melt  away,  the  sea  enters  to  form  long, 
narrow,  steep-walled  re-entrants,  CdXXed  fiords,  Norway  (Fig.  176), 
Scotland,  Maine,  and  Alaska  have  fiord  coasts,  though  all  of  them 
owe  their  characteristics  in  part  to  sinking.     Many  islands  front 


CHARACTERISTICS  OF  GLACIAL  DEPOSITS       257 


these  coasts,  most  of  them  representing  the  higher  parts  of  the  old 
land  whose  surroundings  have  been  drowned. 

GLACIAL  DEPOSITS 

General  characteristics.  Most  of  the  material  transported  by 
a  glacier  is  carried  in  its  lower  part;  but  some  is  carried  in  the  ice 
above  its  bottom,  and  some  on  top  of  the  ice.    All  of  it  is  left,  finally,- 


Fig.  174,    Hanging  valley;  Nunatak  Fiord,  Alaska.    (Tarr,  U.  S.  Geol.  Surv.) 

on  the  surface  of  the  land.  The  materials  deposited  by  glaciers,  called 
glacial  drift  or  till,  range  from  finest  earth  to  huge  bowlders  (Fig.  177). 
They  are  not  stratified, 
and  in  many  places  are 
so  deposited  as  to  form 
distinctive  topographic 
features.  Much  of  the 
drift  deposited  by  the 
continental  glaciers  is 
a  thorough  mixture  of 
many  kinds  of  mate- 
rial, for  it  was  derived 
from  a  vast  area  within 
which  many  kinds  of 
rocks  occur.  (Com- 
pare glacial  drift  with 
stream  deposits.) 

Leading  tjrpes.     When  the  end  of  a  valley  glacier  or  the  edge  of 
an  ice-cap  stays  in  the  same  place  for  a  long  time,  a  thick  body  of 


Fig.  175.  A  hill  smoothed  by  the  glacier  ice 
which  overrode  it.  Shore  of  North  Greenland. 
(From  photograph  by  Chamberlin.) 


^58 


MODIFICATION  OF  LAND  SURFACES 


drift  is  lodged  beneath  it,  for  drift  is  brought  to  this  position  all  the 
time  by  the  oncoming  ice,  and  left  there.  Such  a  deposit  is  a  terminac 
moraine  (Fig.  178).  All  the  other  drift  deposited  by  an  ice-sheet  is 
ground  moraine.     After  a  glacier  melts,  the  area  of  ground  moraine  is 


Fig.  176.     The  Sogne  Fiord,  coast  of  Norway.     (Robin.) 


not  a?  great  as  the  glaciated  area,  for  glaciers  do  not  carry  debris  in  all 
parts  of  their  bottoms.  In  general,  the  drift  is  thickest  and  covers 
the  largest  proportion  of  the  surface  near  the  margins  of  a  glaciated 
area,  and  is  thinnest  and  least  continuous  in  the  region  from  which 

the  ice  spread  (Why?). 
For  this  reason,  there 
are  large  areas  of  bare 
rock  and  of  thin,  bowl- 
der-strewn soil  on  the 
uplands  of  eastern  and 
northeastern  Canada. 
Together  with  a  bleak 
climate,  these  condi- 
tions render  large  areas 
unfit  for  farming. 
Much  of  the  material 
removed  by  the  ice 
from  Canada  was  de- 
posited in  the  United 
States.  The  lateral 
moraines  are  left  along  the  sides  of  a  valley  after  the  valley  glacier 
is  melted  (Fig.  179).     Some  of  them  are  hundreds  of  feet  high. 

Surface  features.     Because  glaciers  distribute  their  drift  very 
unevenly,  large  areas  once  covered  by  ice  are  marked  by  hillocks, 


' ''.-.^  •  .r^^ 

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^^igKC£LL9K:kmemm 

»•••./.-.•- 

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f^^ill; 

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r'Jf:''''i     '' 

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^d 

■B'^y     '-         *"T"^MliTiai — tmm  \ 

"wJN^ 

■,J^    Wl 

w^  -.  ■  -  'v^; j^mnHig^ 

'■■•i-Y 

kY^£ 

'A    mm\ 

Fig.  177.     Section    of    unstratified    drift    near 
Henry,  Illinois.     (Crane.) 


SURFACE  FEATURES  DUE  TO  ICE  DEPOSITS     259 

mounds,  and  ridges  of  drift,  and  by  basin-like  or  trough-like  depres- 
sions. These  features  are  most  pronounced  in  terminal  moraines, 
the  surfaces  of  which  may  be  distinctly  rough  and  hummocky  (Fig.  1 80) . 


Fig.  178.     A  glacier  in  the  Cascade  Mountains,  Washington.    Shows  spreading 
end  of  glacier,  crevasses  in  ice,  and  terminal  moraine.    (Willis,  U.  S.  Geol.  Surv.) 


In  the  Lake  States,  the  rougher  parts  of  the  terminal  moraines 
commonly  are  used  for  woodlots  and  pastures  (p.  173),  for  the  sur- 
face is  too  uneven  and  the  soil  too  coarse  and  stony  to  be  cultivated 
successfully,  in  competition  with  the  neighboring  prairies.  Many 
of  the  hollows  in  the  surface  of  the  drift  contain  lakes  (p.  261),  ponds, 


26o 


MODIFICATION  OF  LAND   SURFACES 


and  marshes  (p.  300).     It  is  estimated  that  there  are  4>^  millioii 
acres  of  marsh  land  in  Minnesota,  nearly  as  much  in  Michigan,  and 

2y^  million  in  Wiscon- 
sin. The  total  swamp 
area  for  the  three 
states  is  larger  than 
the  combined  area 
of  Massachusetts, 
Connecticut,  Rhode 
Island,  and  Delaware. 
Nearly  all  this  swamp 
land  is  the  result  of 
glaciation. 

The  surface  of  the 
drift   is   very   unlike 
that  developed  by  the 
erosion  of  running  water,  for  in  the  latter  the  depressions  have  out- 
lets, and  the  hills  and  ridges  stand  in  a  definite  relation  to  the  valleys. 
The  drift  left  by  the  continental  glacier  increased  the  relief  in 
some  places  (Fig.  181),  with  unfavorable  results;  but  in  most  places 


Fig.  179.  A  lateral  moraine  left  by  a  former 
glacier  in  the  Bighorn  Mountains  of  Wyoming. 
(From  photograph  by  Blackwelder.) 


^r^ 

- 

■i  ^KBfjt^ 

^^^Hk-rv:;. 

'W^ 

i 

"^'  !tf>i3gy 

IH 

9b9^^ 

«■ 

^m 

^^^^^^^^^^^Hk^.j^Ll 

fr^l^^2^*j 

^ygggjjl 

g^^i^l^^HH 

Fig.  1 8c    Terminal  moraine  topography  near  Oconomowoc,  Wis.    (Fenneman.) 

it  decreased  relief  and  left  the  surface  less  rough  than  before 
(Fig.  182).  This  made  it  easier  to  cultivate  the  land  and  to  build 
roads.     Most  of  the  surface  between  the  Ohio  River  and  the  Great 


FORMATION  AND   DESTRUCTION  OF  LAKES      261 


Fig.  181. 


Lakes  appears  to  have  been  made  smoother.  But  for  glaciation, 
much  of  this  region  probably  would  have  a  maturely  eroded  sur- 
face, not  unlike  that 
of  the  driftless  area, 
and  a  poorer  soil  than 
it  now  has. 

Deposits  beyond 
the  land.  Glaciers 
which  descend  into  the 
sea  may  build  subma- 
rine banks  and  even 
islands.  Along  the 
eastern  coast  of  North 
America,  these  deposits 
may  have  reached  the  Fig.  182. 

edge  of  the  continental  Fig.  181.     Diagram  showing  how  a  nearly  level 

shelf    in    some    places      surface  may  be  replaced  by  a  rough  one  through  the 

,      ,        \T-  j'     uneven  deposition  of  drift. 

Marthas      Vineyard,  pig.  182.     Diagram  showing  how  glacial  drift 

Nantucket,   and    Long     may  replace  a  hilly  surface  with  a  fairly  level  one. 
Island    are    composed 

largely    of    drift.     The    sheltered    waterway    behind    Long    Island 
favored  the  early  growth  of  sea  interests  in  southern  New  England. 


49-, 


j3  Miles 


Fig.  183.  Map  showing  the  abundance  of  lakes  in  parts  of  the  glaciated  area. 
(From  Barrett,  Minnesota,  Sheet,  U.  S.  Geol.  Surv.) 

Glacial  lakes.  The  thousands  of  lakes  in  northern  United 
States  (Fig.  183)  and  Canada  are  nearly  all  of  glacial  origin.  Some 
are  in  basins  gouged  out  of  the  bed-rock  (Fig.  184);  some  are  in  the 


962 


MODIFICATION  OF  LAND  SURFACES 


Fig.  184.    Section  of  a  lake  in  an 
ice-scoured  rock  basin. 


unfilled  portions  of  drift-choked  preglacial  valleys;  and  many  are  in 

hollows  in  the  surface  of  the  drift  (Fig.  185).     The  terminal  moraines 

of  many  valley  glaciers  form  dams,  ponding  the  waters  of  the  streams 

above,  making  lakes  (Fig.  186). 

The  smaller  and  shallower  of  these  lakes  and  ponds  are  being  destroyed  rapidly 
by  (i)  the  sediment  washed  into  them  from  the  tributary  slopes,  and  (2)  vegetable 
matter.  Some  are  being  drained  slowly  (Why  slowly?)  by  the  erosion  of  their 
outlets,  in  the  future,  many  of  the  shallower  ones  will  be  drained  by  man,  that 
he  may  use  their  bottoms  as  farm  land.  It  has  been  estimated  that  there  are 
8,000  lakes,  big  and  little,  in  Minnesota,  and  that  half  of  them  will  be  destroyed 

by  natural  processes  wi'^hin  fifty  years. 
Connecticut  has  been  credited  with  hav- 
ing had  some  4,000  lakes  at  the  close  of 
the  Glacial  Period;  2,500  of  them  have 
been  destroyed,  and  the  sites  of  many 
of  them  now  form  choice  garden  spots. 
In  southern  Michigan  and  Wisconsin 
many  early  settlers  located  their  farms 
on  the  bottoms  of  former  lakes,  attracted 
by  the  flat  land  and  the  fine,  easily- 
worked  soil. 

Deposits  of  marl  occur  in  and  about 
some  glacial  lakes.  This  marl  is  a  soft, 
limey  earth,  the  calcium  carbonate  of 
which  is  contributed  chiefly  by  the  shells 
of  fresh-water  mollusks  and  by  lime- 
secreting  lake  plants.  In  parts  of  Mich^ 
igan  and  northern  Indiana,  these  deposits 
are  used  in  making  Portland  cement. 

The  lakes  and  swamps  of  the 
glaciated  region  make  the  streams 
flow  more  steadily  through  the 
year  by  holding  back  some  of  the  water  of  wet  times,  letting  it  flow 
out  in  times  of  drought.  The  drift  itself  exerts  a  similar  influence, 
for,  on  the  whole,  it  is  thicker  than  the  mantle  rock  of  other  regions, 
and  therefore  absorbs  more  water,  which  it  yields  up  slowly,  making 
the  supply  of  ground-water  to  streams  more  steady  than  it  would 
be  otherwise.  Thus  floods  are  less  numerous  and  less  dangerous,  and 
the  value  of  the  streams  for  navigation  and  power  is  increased. 
By  reducing  or  preventing  floods,  the  porous  drift  and  the  lakes  also 
greatly  reduce  soil  erosion. 

Certain  lakes  which  came  into  existence  along  the  margin  of 
the  continental  glacier  disappeared  with  the  ice.  One  of  the  largest 
of  the  marginal  lakes  (Lake  Agassiz)  lay  in  the  valley  of  the  Red 


Fig.  185.     Section  of  a  lake  lying 
in  a  hollow  in  the  surface  of  the  drift. 


Fig.  186.    Section  of  a  lake  behind 
a  barrier  of  drift. 


LAKE  AGASSIZ 


263 


River  of  the  North  (Fig.  187).  This  lake  covered  an  area  greater 
than  that  of  all  the  Great  Lakes.  The  water,  however,  was  shallow. 
It  came  into  existence  when  the  edge  of  the  retreating  ice  lay  north  of 
the  lake,  and  blocked  drainage  in  that  direction.  The  water  rose  in 
the  basin  until  it  overflowed  to  the  south,  finally  reaching  the  Missis- 
sippi River.     When  the  ice  at  the  north  melted  back  far  enough,  a 


,^O-DS0Il     5 


/"^^/L.    .... 


"^  ,-• 


Fig.  187.  Map  of  extinct  Lake  Agassiz,  and  other  glaciallakes.  Lake  Winni- 
peg occupies  a  part  of  the  basin  of  Lake  Agassiz.     (U.  S.  Geol.  Surv.) 

new  and  lower  outlet  was  opened  to  Hudson  Bay,  and  the  lake  was 
drained.  Lake  Winnipeg  and  several  smaller  lakes  may  be  regarded 
as  remnants  of  Lake  Agassiz,  for  they  occupy  the  deepest  parts  of  the 
old  basin. 

As  late  as  1870  the  floor  of  extinct  Lake  Agassiz  was  almost 
unoccupied  by  farmers  (Fig.  188),  but  during  the  next  few  years 
its  soil  was  found  to  produce  a  fine  grade  of  hard  wheat,  and  a  great 
tide  of  farm-seekers  turned  to  the  region  (Fig.  189).  On  the  nearly 
level  lake  floor  it  was  possible  to  plow  league-long  furrows  in  straight 
lines,  and  later  to  do  much  of  the  work  by  such  labor  saving  machines 


264 


MODIFICATION  OF  LAND   SURFACES 


as  the  steam  plow.  Ft.  Gary  quickly  grew  into  the  city  of  Winnipeg, 
and  the  wheat  of  the  region  helped  to  make  Minneapolis  the  leading 
flour  manufacturing  city  of  the  United  States  (p.  288). 

The  Great  Lakes  did  not  exist,  so  far  as  known,  before  the  Glacial 
Period,  but  river  valleys  probably  extended  along  their  longer  diam- 
eters. Lake  basins  were  made  as  a  result  of  (i)  the  deepening  of  these 
valleys  by  ice  erosion,  (2)  the  building  up  of  the  rims  of  the  basins 


1870   1 

"^     1 

MINNESOTA 

1         r^           (^ 

DAKOTA  J       te^^-''^^^^^>4^r^^ 

\Jli^^^ 

__jij&^^ 

Fig.  188.  Fig.  189. 

Fig.  188.     Map  showing  distribution  of  population  in  region  of  Red  River  of 
the  North  in  1870. 

Fig.  189.     Population  map  of  region  of  Red  River  of  the  North  in  1880. 


by  the  deposition  of  drift,  and  perhaps  (3)  the  down-warping  of  the 
sites  of  the  basins.  The  influence  of  the  Great  Lakes  on  cHmate  and 
on  certain  industries  has  been  noted  in  earlier  connections.  Their 
importance  as  commercial  highways  is  considered  in  Chapter  XVI. 

Hundreds  of  the  glacial  lakes  are  of  great  benefit  to  man  as  pleasure  and 
health  resorts,  and  as  sources  of  water  supply.  Many  have  become  famous  through 
their  fine  summer  residences,  and  very  many  more  are  visited  by  numerous  camping, 
boating,  and  fishing  parties.  In  these  ways  the  lakes  have  become  large  factors  for 
good  in  the  life  of  the  people. 

Effect  of  ice  deposits  on  stream  courses.  The  deposition  of 
drift  filled  many  of  the  former  valleys.  After  the  ice  melted,  the 
surface  drainage  followed  the  lowest  lines  open  to  it;  but  these  lines 
did  not  always  correspond  with  the  former  valleys,  for  some  of  the 
latter  had  been  filled,  and  most  of  them  were  blocked  up  in  some  places. 


BENEFITS  RESULTING  FROM  GLACIATION        265 


The  surface  waters  therefore  followed  former  valleys  in  some  cases, 
and  in  others  flowed  where  there  had  been  no  valleys.  In  choosing 
their  new  courses,  the  streams  in  places  ran  down  steep  slopes  or 
fell  over  cliffs.  Many  of  the  rapids  and  falls  of  the  glaciated  area, 
so  important  in  the  economic  life  of  the  country  (p.  288),  came  into 
existence  in  this  way. 

Glacial  soils.  In  the  United  States,  glaciation  increased  the 
amount  of  mantle  rock,  and  improved  the  quality  of  the  soil  in 
many  places.  Much  of  the  latter  is  good  because  it  is  a  thorough 
mixture  of  material  derived  from  many  kinds  of  rock,  and  so  is  well 
supplied  with  all  the  mineral  elements  necessary  for  plants  (p.  169). 
It  is  instructive  to  compare  Fig.  257,  showing  the  relation  of  the  im- 
proved acreage  to  the  total  farm  acreage  in  the  different  states,  with 
the  map  showdng  the  glaciated  area  (Fig.  170).  Iowa,  Illinois,  Indi- 
ana, and  Ohio  are  seen  to  lead 
in  the  relative  amount  of  their 
improved  land.  Glaciation  is 
perhaps  the  most  important 
fact  in  the  geography  of  each 
of  these  states,  and  it  has 
greatly  furthered  their  high 
rank  in  agriculture. 

The  benefits  which  the  states 
between  the  Ohio  River  and  the 
Great  Lakes  received  from  glaciation 
may  be  illustrated  further.  Fig.  190 
shows  the  glaciated  and  unglaciated 
parts  of  Ohio.  The  unglaciated  part 
belongs  to  the  Alleghany  Plateau. 
It  is  in  a  mature  stage  of  erosion,  and 
the  thin,  sandy  soils  on  the  steep 
slopes  wash  easily.  The  first  settle- 
ment in  Ohio  was  made  in  this  part 
of  the  state,  at  Marietta;   but  soon 

the  tide  of  settlement  set  toward  the  more  attractive  glacial  plains  farther  west  and 
north,  and  the  population  of  most  of  the  unglaciated  counties  remained  relatively 
sparse  until  the  mineral  resources  of  the  region  were  developed.  Many  farmers  in 
the  unglaciated  section  turned  their  attention  to  sheep-raising  when  they  found 
they  could  not  grow  grain  for  export  in  competition  with  the  farms  of  the  glaciated 
area,  and  grazing  was  long  an  important  industry  in  the  southeastern  part  of 
the  state. 

About  four-fifths  of  Indiana  were  glaciated.     On  the  average,  the  glaciated 
land  is  worth  about  twice  as  much  as  the  unglaciated,  and  the  yields  of  staple 


Fig.  iQo.    Map  showing  the  glaciated 
(shaded)  and  unglaciated  portions  of  Ohio. 


266  MODIFICATION  OF  LAND  SURFACES 

crops  bear  a  similar  relation.  The  southern  boundary  of  the  region  within  which 
4,500  bushels  of  corn  are  grown  per  square  mile  is  the  margin  of  the  latest  drift 
sheet.     The  situation  is  much  the  same  in  Illinois. 

The  quality  of  the  soil  in  places  was  injured  by  glaciation.  In 
some  of  these  places  the  drift  isvery  thin,  while  in  others  it  is  very  stony, 
so  that  great  labor  is  necessary  to  put  it  in  workable  condition. 
Again,  the  drift  may  be  too  sandy  or  gravelly  to  make  good  soil,  or 
its  surface  may  be  too  rough  (pp.  173,  259). 

Special  uses  of  glacial  deposits.  Much  drift  clay  (rock  flour)  is  used  for  mak- 
ing brick,  tile,  and  other  clay  products.  Ohio  has  been  the  leading  state  in  the  clay 
industry  for  many  years,  because  of  the  abundance  of  raw  clay,  part  of  which  is 
drift,  cheap  near-by  fuel,  excellent  shipping  facilities,  and  nearness  to  great  markets. 
About  1,000,000,000  bricks  are  made  from  glacial  clay  each  year  in  the  vicinity  of 
Chicago.  The  gravel  of  the  drift  is  used  extensively  for  road  making,  and  in  the 
manufacture  of  various  kinds  of  cements. 

DEPOSITS  BY  GLACIAL  WATERS 

Water  flows  in  abundance  from  all  glaciers  in  the  summer,  and 
from  many  glaciers  all  the  time.  Stream  work,  therefore,  accom- 
panies glaciation  in  all  cases,  and  much  of  the  drift  left  by  ice  is 
modified  by  water  afterward. 

Streams  which  flow  from  glaciers  carry  so  much  sediment  that 
in  many  cases  they  build  gravelly  or  sandy  plains  beyond  the  ice. 
Such  a  deposit  in  a  valley  below  a  glacier  is  a  valley  train.  Valley 
trains  are  developed  best  just  outside  terminal  moraines.  The 
Rock  River,  in  southern  Wisconsin,  filled  its  valley  with  gravel  and 
sand  to  a  depth  of  300  to  400  feet  just  outside  the  terminal  moraine 
of  the  last  glacial  epoch.  The  Columbia  River  filled  its  valley 
to  the  depth  of  700  feet  in  places  \vith  sediment  washed  out  from  the 
ice.  Since  the  ice-sheet  melted,  parts  of  most  of  the  valley  trains  have 
been  carried  away,  and  their  remnants  are  terraces  (Fig.  162).  Drift 
terraces  are  common  features  of  many  of  the  valleys  of  south-flowing 
rivers  in  the  glaciated  area  and  just  south  of  it. 

Streams  which  issue  from  an  ice-sheet  and  fail  to  find  valleys 
build  alluvial  fans.  By  growth,  these  fans  may  unite,  making  an 
outwash  plain,  very  much  like  a  compound  alluvial  fan.  Like  valley 
trains,  outwash  plains  are  developed  best  just  outside  the  terminal 
moraines  of  ice-sheets,  and  their  materials  are  stratified.  East  New 
York,  Woodhaven,  Jamaica,  and  other  suburbs  of  Brooklyn  grew  up 
on  the  outwash  plain  of  Long  Island  before  the  terminal  moraine 


DEPOSITS   BY   GLACIAL  WATERS  267 

just  to  the  north  was  much  settled.  (What  were  the  probable  rea- 
sons for  this?) 

Deltas  may  be  built  in  lakes  at  the  ends  or  edges  of  glaciers, 
and  the  deposits  made  by  waters  beneath  the  ice  and  at  its  edge 
take  on  locally  the  form  of  ridges  and  hillocks. 

As  a  glacier  melts  away,  the  waters  produced  by  the  melting 
flow  over  the  surface  of  the  drift  which  the  ice  had  deposited,  and 
modify  it  more  or  less  by  eroding  in  some  places  and  depositing 
in  others.  As  a  result  of  all  these  phases  of  water  work,  much  of 
the  drift  is  stratified. 

Summary.  Although  less  important,  ice  takes  its  place  with  air 
and  water  as  one  of  the  three  agents  which  modify  land  surfaces. 
From  this  standpoint,  its  principal  mission  is  the  wearing  of  the  land 
and  the  moving  of  the  waste  toward  the  sea.  Through  their  wide- 
spread effects  on  topography,  soil,  drainage,  and  the  distribution  of 
plant  and  animal  life,  the  ancient  ice-sheets  are  far  more  important 
than  the  glaciers  of  to-day,  as  factors  in  human  affairs.  Existing 
glaciers  are  valuable  to  man  chiefly  in  connection  with  the  develop- 
ment of  power  on  the  streams  which  flow  from  them. 


QUESTIONS 

1.  In  northern  United  States  and  Canada,  would  floods  which  occur  as  the 
river  ice  breaks  up  in  spring  be  more  likely  to  be  disastrous  on  north-flowing  or 
south-flowing  streams?     Why? 

2.  Why  are  there  more  glaciers  in  the  Sierra  Nevada  and  Cascade  mountains 
than  in  the  Rocky  Mountains?     Why  are  there  more  in  Montana  than  in  Colorado? 

3.  State  all  the  factors  which  influence  the  size  of  a  valley  glacier. 

4.  Compare  and  contrast  typical  topographies  due  to  (i)  glaciation  and  (2) 
river  erosion. 

5.  (i)  W^hat  are  all  the  important  ways  in  which  human  interests  have  been 
(a)  benefited  and  (b)  injured  by  the  work  of  the  ancient  ice-sheets  in  the  United 
States?     (2)  On  the  whole,  was  glaciation  beneficial  or  injurious? 

6.  Why  are  the  effects  of  glaciation  more  favorable,  from  the  standpoint  of 
man,  in  northern  United  States  than  in  northeastern  Canada? 


CHAPTER  XVI 
THE   USES  AND   PROBLEMS   OF   INLAND  WATERS 

Many  ways  in  which  streams  and  lakes  affect  human  interests 
have  been  noted  in  preceding  pages.  In  the  present  chapter,  inland 
waters  are  considered  from  the  standpoints  of  navigation,  power, 
irrigation, drainage,  and  water  supply. 

Navigation 

In  the  early  development  of  many  countries,  lack  of  roads  led  to 
the  use  of  the  waterways  for  trade  and  travel.  Even  after  roads 
had  been  built,  transportation  by  water  was  much  cheaper  than 
transportation  by  land  in  most  cases,  and  trafl&c  continued  to  use 
waterways  where  they  were  available.  Where  railroads  have  come 
into  competition  with  waterways,  the  latter  in  most  cases  have  lost 
much  of  their  traffic.  The  waterways  of  some  countries  have  been 
protected  by  law  against  ruinous  railroad  competition,  and  certain 
waterways,  for  example  the  Great  Lakes,  furnish  such  favorable 
conditions  for  transportation  that  their  traffic  has  grown  in  spite 
of  the  railroads.  The  average  cost  of  hauling  over  the  railroads  in 
the  United  States  decHned  from  7^3  cents  a  ton  per  mile  in  1837, 
to  less  than  4/5  of  a  cent  per  mile  in  1905;  yet  under  favorable  con- 
ditions, the  cost  of  transportation  by  water  is  estimated  to  be  only 
V4  to  ^3  that  by  rail.  In  1909,  rates  for  iron  ore  on  the  Great  Lakes 
were  less  than  one  mill  a  ton  per  mile,  while  the  rates  for  ore  by  rail 
were  about  one  cent  a  ton  for  the  same  distance. 

RIVER  NAVIGATION 

Streams  were  the  first  waterways  to  be  used  regularly  for  com- 
merce. The  Euphrates  and  Nile  were  among  the  rivers  to  which  men 
first  entrusted  themselves  and  their  goods.  After  a  time,  river 
navigation  led  to  coastwise  navigation,  but  to  the  end  of  the  Mediaeval 
Period  there  was  little  or  no  navigation  of  the  open  ocean.  It  is 
only  in  the  Modern  Period  that  navigation  of  the  open  sea  has  per- 
mitted the  development  of  world-wide  commerce. 

?6X 


THE   GREAT  RIVERS  OF  THE  WORLD  269 

Leading  rivers  of  foreign  lands.  Because  of  its  relief  (p.  24), 
few  of  the  rivers  of  Asia  are  important  highways  of  commerce.  The 
Yang-tze  is  the  greatest  highway.  Fed  by  the  snow-fields  of  the 
mountains  of  Tibet,  and  flowing  to  the  Pacific  through  some  of  the 
most  densely  populated  provinces  of  China,  it  is  both  one  of  the  long- 
est rivers  in  the  world,  and  one  of  the  most  important  commercially. 
Large  ocean  steamers  go  up  600  miles  to  Hankow;  smaller  steamers 
ply  the  river  500  miles  farther,  to  the  mouth  of  the  gorges;  and 
native  junks  go  up  many  miles  more.  The  Hwang-ho,  the  other 
great  river  of  China,  flows  through  a  densely  settled  region,  but  is 
nearly  useless  for  navigation  because  of  its  shifting  and  silt-choked 
channel. 

In  India,  the  Ganges  and  Indus  present  a  contrast  similar  to  that 
of  the  Yang-tze  and  Hwang-ho.  The  Ganges  traverses  the  most 
populous  and  wealthy  provinces,  and  has  been  of  great  significance 
throughout  the  history  of  India.  It  is  fed  by  many  Himalayan  tor- 
rents, and  flows  for  about  1 200  miles  across  the  alluvial  plains  of  the 
north.  Ocean  steamships  ascend  the  Hugh,  one  of  the  mouths 
of  the  Ganges,  to  Calcutta,  and  the  river  is  used  more  or  less  for 
navigation  to  the  base  of  the  mountains.  The  Indus  River  is  used 
but  little  by  steamers,  because  of  many  sand  bars  and  frequent 
changes  in  the  channel.  Together  with  its  larger  tributaries,  it  is 
valuable  chiefly  for  irrigation.  The  great  rivers  of  Siberia  are  navi- 
gable for  hundreds  of  miles,  but  their  value  is  lessened  because  they 
flow  to  the  Arctic  Ocean. 

The  relief  of  Africa  limits  the  navigation  of  most  of  its  rivers  to 
relatively  short  distances  (p.  25).  The  Nile  has  regular  steamboat 
service  to  the  First  Cataract,  but  navigation  is  not  easy  in  the  delta 
portion  of  the  river  below  Cairo.  Above  the  cataracts,  the  river  is 
navigable  throughout  the  year  for  long  distances. 

Throughout  the  history  of  Russia  its  rivers  have  been  its  chief 
highways.  Even  to-day,  they  have  greater  relative  importance 
than  the  rivers  of  western  Europe,  because  other  means  of  trans- 
portation are  less  satisfactory;  wagon  roads  are  poor  and  railroads 
few.  Most  of  the  Russian  rivers  rise  in  the  vicinity  of  the  Valdai 
Hills  and  follow  long  courses  across  low,  nearly  level  plains.  Their 
currents,  therefore,  ordinarily  are  gentle.  They  are  navigable  through- 
out most  of  their  courses,  and  the  diff'erent  systems  have  been  joined 
by  canals,  so  that  there  is  water  connection  between  the  Caspian, 
Black,  Baltic,  and  White  seas.    While  the  above  conditions  are 


270      USES  AND  PROBLEMS  OF  INLAND   WATERS 

favorable  to  commerce,  navigation  of  the  Russian  rivers  is  attended 
by  serious  drawbacks.  They  are  ice-locked  in  winter  (p.  246), 
subject  to  great  floods  in  spring,  affected  by  sand  bars  which  hinder 
navigation  at  low  stages,  and  most  of  them  are  tributary  to  inland 
seas.  The  Volga  is  the  most  important  Russian  river,  and  the 
largest  river  of  Europe.  Together  with  its  tributaries,  it  is  said  to 
afford  7,500  miles  of  navigation.  Its  usefulness  is  lessened  by  the  fact 
that  its  lower  course  is  through  a  semi-arid  region,  and  by  the  fact 
that  it  ends  in  a  land-locked  sea. 

Most  of  the  larger  rivers  of  central  and  western  Europe  are 
important  commercially,  and  large  sums  have  been  spent  to  improve 
them  and  extend  their  connections  by  canals.  In  Germany,  river 
transportation  increased  more  than  fivefold  in  the  thirty  years 
preceding  1905,  although  Germany  has  a  greater  railroad  mileage  than 
any  other  country  in  Europe.  This  is  in  striking  contrast  with  the 
situation  in  the  United  States  (p.  278).  The  rivers  and  canals  of 
Germany  (p.  287)  furnish  from  8,000  to  10,000  miles  of  navigable 
waterways.  So  much  work  has  been  done  in  dredging,  straightening, 
and  otherwise  improving  the  larger  rivers,  that  it  is  said  scarcely  one 
of  them  flows  in  a  natural  channel. 

The  Rhine  has  influenced  the  history  of  Germany  more  than  any 
other  river,  and  is  to-day  the  most  important  commercial  river  in 
Europe.  Fed  by  melting  snows  in  Switzerland  and  made  steady  in 
its  flow  by  passing  through  Lake  Constance,  it  flows  through  western 
Germany  and  the  Netherlands,  into  the  North  Sea.  Rotterdam, 
on  the  Rhine  delta,  is  one  of  the  greatest  ports  of  continental  Europe, 
and  Cologne,  though  far  inland,  is  practically  a  seaport.  The  fertile 
valley  of  the  Rhine  is  settled  densely.  Commercially,  the  Elbe  is 
the  second  river  of  Germany,  though  much  less  important  than  the 
Rhine.  The  trafl&c  on  these  rivers  is  largely  in  heavy  freight,  such  as 
coal  and  grain. 

The  Danube  has  been  an  important  highway  since  early  times. 
Like  many  other  delta-building  rivers,  it  was  difi&cult  to  enter  until 
jetties  were  built  at  its  mouth.  Extensive  improvements  have  been 
made  also  at  the  "Iron  Gate,"  and  elsewhere.  The  Rhone  is  the 
largest  river  of  France,  and  its  valley  is  the  natural  highway  into  the 
country  from  the  south.  Navigation  in  the  delta  portion  of  the  stream 
was  hindered  by  shallow  and  shifting  channels,  and  large  sums  have 
been  spent  in  improvements.  Even  now,  however,  the  Rhone  is  not 
navigable  for  large  ships.     The  Po  and  the  Ebro  are  the  only  other 


THE   GREAT  RIVERS  OF  THE  WORLD 


271 


European  streams  of  importance  flowing  into  the  Mediterranean, 
and  neither  is  used  much  for  navigation. 

In  Great  Britain,  the  rivers  are  comparatively  short,  but  their 
value  is  increased  by  the  fact  that  their  lower  courses  are  drowned, 
and  subject  to  rather  high  tides.  The  tides  help  to  make  Liverpool 
and  London  great  seaports,  though  both  are  on  small  rivers.  Like 
the  United  States,  Great  Britain  has  neglected,  till  recently,  the 
question  of  waterway  improvement.  To-day  transportation  in  Eng- 
land is  said  to  be  the  most  expensive  in  Europe. 


Fig.  191.  Map  showing  principal  streams  in  the  United  States  actually  used 
for  purposes  of  transportation  (1906).  Only  the  parts  so  used  appear  on  the  map. 
(Data  from  map  by  U.  S.  Bureau  of  Corporations.) 

The  Amazon  is  the  largest  river  in  the  world,  with  a  length  of 
about  4,000  miles.  Ocean  steamers  can  go  up  1,000  miles,  and  with 
its  29  large  tributaries  it  furnishes  more  than  20,000  miles  of  navigable 
water,  most  of  it  through  dense  forests.  The  river  is  used  to  carry 
out  tropical  woods,  rubber,  and  other  products.  The  Orinoco  is 
navigable  for  small  boats  to  within  100  miles  of  Bogota,  and  the  La 
Plata  System  is  navigated  by  steamers  for  long  distances.  . 

Besides  the  great  rivers  mentioned  above,  there  are  many  others 
which  serve  as  highways  of  trade  and  travel. 

Navigable  streams  of  the  United  States.  There  are  about  300 
streams  in  the  United  States  that  are  navigated  more  or  less  (Fig. 


272      USES  AND   PROBLEMS  OF  INLAND   WATERS 

iQi).  Their  total  navigable  length  is  about  26,400  miles  —  more 
than  the  circumference  of  the  earth.  Only  a  few  have  much  com- 
mercial importance  now,  and  many  are  used  only  by  small  boats 
engaged  in  local  trade.  As  Fig.  igi  shows,  most  of  the  navigable 
streams  are  in  the  eastern  half  of  the  country.  The  absence  of 
navigable  waterways  (Why  absent?)  has  been  a  serious  disadvantage 
to  much  of  the  West. 

The  principal  rivers,  and  the  part  which  they  have  played  in 
the  development  and  commerce  of  the  country,  are  discussed  briefly 
in  the  following  paragraphs.  Most  attention  is  given  to  the  Mis- 
sissippi System,  because  it  is  by  far  the  most  important. 

Atlantic  Rivers  of  United  States 
On  the  Atlantic  slope  there  are  nearly  150  streams  navigable 
for  varying  distances  from  the  sea  —  in  most  cases  only  to  the  head 
of  tide-water.    The  rivers  of  New  England  are  navigable  for  short 
distances  only,  because  of  falls  and  rapids. 

The  Connecticut  is  navigable  to  Hartford;  the  Merrimac  to  Haverhill;  the 
Saco  to  Saco  and  Biddeford;  the  Kennebec  to  Augusta;  and  the  Penobscot  to 
Bangor.  All  these  cities  receive  much  freight  by  water.  Many  streams  of  central 
and  northern  New  England  are  used  for  rafting  lumber  and  floating  logs. 

Although  the  streams  of  New  England  afford  little  navigation,  the  larger  val- 
leys have  been  important  highways  since  the  settlement  of  the  region  began.  They 
guided  fur  traders,  lumbermen,  and  farmers  (p.  219)  into  the  interior.  They 
served  as  lines  of  advance  and  retreat  for  Indian  war  parties  and  colonial  armies. 
General  Arnold  invaded  Canada  in  1775  by  way  of  the  Kennebec  and  Chaudi^re 
valleys.  To-day  many  of  the  valleys  are  followed  by  railroads.  Boston  was 
handicapped  greatly  in  its  commercial  development  by  the  fact  that  no  large, 
navigable  river  came  to  it  from  the  interior. 

The  Hudson  is  the  most  important,  commercially,  of  the  tribu- 
taries to  the  Atlantic  from  the  United  States.  Because  the  Hudson 
Valley  is  drowned,  deep  water  extends  100  miles  inland,  and  the  river 
is  navigable  50  miles  farther,  to  Troy. 

The  belt  of  relatively  weak  rocks  along  which  the  Hudson  Valley  developed 
contains,  farther  north,  Lake  Champlain  and  the  Richelieu  River.  This  long, 
narrow  lowland,  which  extends  from  New  York  City  to  the  St.  Lawrence  River 
near  Montreal,  was  called  by  the  Indians  "The  Grand  Passway."  General 
BurgojTie  (1777)  and  General  Prevost  (1814)  used  it  to  invade  the  United  States. 
When  the  Champlain  Canal  was  opened  between  the  Hudson  River  and  Lake 
Champlain,  water  transportation  was  possible  throughout  its  entire  length.  The 
Mohawk  Valley  and  the  low  plain  to  which  it  leads  furnish  an  easy  route  between 
the  Hudson  River  and  Lake  Erie;  the  highest  point  is  only  445  feet  above  sea-levei. 


RIVERS  AS  FACTORS   IN  COLONIAL  LIFE 


273 


more,    Richmond, 


NewYt(rk 

>^ 
Trenton^ 

Philadelphia 


,■ — Balfitpori 

iWasfiingto- 


Its  drowned-valley  harbor  and  good  connection  with  the  interior  have  been  leading 
factors  in  the  growth  of  New  York  City. 

South  of  the  Hudson  River,  most  of  the  larger  rivers  are  navigable 
to  the  ''fall  line,"  where  the  streams,  in  passing  from  the  hard  rocks 
of  the  Piedmont  Plateau  to  the  weak  rocks  of  the  Coastal  Plain,  have 
developed  falls  and  rapids.    Along  this  line  are  Philadelphia,  Balti- 

Petersburg, 
Columbia,    Augusta, 


Raleigh, 

Macon, andColumbus  (Fig.  192). 
Ocean-going  vessels  ascend  the 
Delaware  River  to  Philadelphia, 
and  smaller  boats  go  up  to 
Trenton.  Several  drowned  trib- 
utaries of  Chesapeake  Bay, 
itself  a  drowned  valley,  have 
some  commercial  importance. 

The  drowned  streams  of  the  Vir- 
ginia region  were  deep  enough  for 
the  light-draft  boats  of  the  colonial 
period,  and  served  the  settlers  as 
roadways.  The  early  plantations  were 
arranged  in  narrow  belts  along  the 
stream  courses.  For  a  century,  travel 
in  tidewater  Virginia  was  largely  by 
water;  little  attention  was  given  to 
road  building.  Ships  came  from  Eng- 
land direct  to  the  wharves  of  many 
of  the  plantations,  to  exchange  for 
tobacco  the  manufactured  goods 
needed  in  the  colony.  Under  these 
circumstances,  no  important  collect- 
ing and  distributing  centers  devel- 
oped. To  1700,  Jamestown  was  the  only  place  worthy  of  being  called  a  village. 
In  South  Carohna,  the  streams  were  not  drowned  sufficiently  to  render  many  of  the 
smaller  ones  navigable.  Hence  Charleston  becam.e  the  commercial  center  of  the 
colony,  and  soon  also  the  social  and  pohtical  center.  In  general,  freight  rates  de- 
crease as  the  size  of  the  cargo  increases,  and  accordingly  the  tendency  has  been  to 
build  larger  and  larger  boats.  As  a  result,  many  of  the  streams  of  the  Coastal 
Plain,  once  important  in  trade,  were  long  since  abandoned  by  commerce. 


Fig.  192.     Map  showing  leading  cities 
along  the  "fall  line." 


Mississippi  River  System 

The  Mississippi  River  has  more  than  50  tributaries  that  were 
navigated  more  or  less  in  1907.  The  navigable  waters  of  the  system 
aggregate  nearly  14,000  miles  and  border  or  traverse   21    states. 


.2  74      USES  AND  PROBLEMS  OF  INLAND  WATERS 

The  Mississippi  River  itself  is  navigable  for  large  steamers  to  St. 
Louis,  and  for  smaller  boats  to  St.  Paul.  The  Ohio  River,  now  much 
the  most  important,  commercially,  in  the  United  States,  is  navigable 
throughout  its  length.  The  Missouri  River  is  navigable  for  small 
boats  to  Ft.  Benton,  in  Montana,  though  it  is  now  used  but  little. 
Other  tributaries  of  the  Mississippi  are  navigable  for  varying  distances, 
as  shown  by  Fig.  191. 

Influence  on  early  development  of  the  West.  At  the  close 
of  the  Revolutionary  War,  the  Mississippi  River  was  made  the 
western  boundary  of  the  United  States,  and  the  supposed  length  of 
the  river  fixed  the  width  (north  and  south)  of  the  country  at  that 
time.  It  was  an  unsatisfactory  international  boundary  line,  for  (i) 
its  position  shifts  (p.  240),  (2)  the  navigation  of  the  river  by  the 
Americans  from  the  east  side  and  any  foreign  people  from  the  west 
side  would  have  led  to  friction,  and  (3)  the  river  basin  is  a  natural 
unit.  The  political  unity  of  the  Mississippi  Basin  was  brought 
about  by  the  Louisiana  Purchase  in  1803. 


Fig.  193.     A  typical  flatboat. 

The  early  western  settlers  could  send  over  the  difficult  mountain 
roads  to  the  eastern  seaports  only  valuable  articles  of  little  bulk  and 
weight,  such  as  whiskey,  furs,  and  ginseng,  or  live  stock,  which  could 
walk  to  market.  For  years,  many  thousands  of  hogs  and  cattle 
were  driven  over  the  mountains  to  Charleston,  Baltimore,  and 
Philadelphia,  but  salted  and  dried  meats,  flour,  tobacco,  and  the  other 
export  products  of  the  frontier  had  to  go  down  the  Mississippi  River 
to  New  Orleans.  Roads  were  few  and  poor,  and  the  settler  found 
It  highly  desirable  to  locate  his  farm  within  easy  hauling  distance 
of  a  navigable  stream.  The  influence  of  navigable  waterways  upon 
the  distribution  of  population  is  shown  clearly  by  the  census  maps 
of  1820  (Fig.  278)   and  several  later  years. 


THE  STEAMBOAT  AND   WESTERN  DEVELOPMENT     275 


One  of  the  most  used  of  the  early  boats  on  the  western  rivers 
was  the  flatboat,  commonly  15  feet  wide  and  40  to  50  feet  long  (Fig. 
193).  While  these  boats  served  for  downstream  navigation,  they 
were  almost  useless  against  the  current  of  the  Mississippi.  Ordinarily 
they  were  broken  up  and  the  lumber  sold  at  New  Orleans.  In  these 
early  days,  freight  was  carried  up-river  largely  in  keel  boats  or  barges. 
Most  of  them  were  equipped  with  oars,  poles,  and  sails,  and  in  many 
cases  they  were  dragged  upstream  by  men  on  the  bank,  tugging  at  a 
long  rope.  The  average  length  of  the  trip  from  New  Orleans  to 
Louisville  was  three  months,  and  in  many  cases  it  required  four 
months. 

Influence  of  steam  navigation  on  the  development  of  the 
Interior.  The  first  steamboat  appeared  on  the  Ohio  River  in  181 1, 
and  within  a  few  years  it  was  seen  that  steamers  could  cope  success- 
fully with  the  currents  of  the  rivers  of  the  Interior,  and  that  they 
would  increase  greatly  the  commercial  value  of  the  streams  (Fig.  194). 


--''  (^iln'r^S^ififfiE??®!: : 


r    .   .^— .      .      ^yi  rilj-^;,    ■  -    6.ii(*ri  ihiihh ,l  l       '       '         ■     — r    —Tj    I^^^E 


Fig.  194.     Mississippi  River  steamboats  at  New  Orleans. 

For  a  time,  they  could  not  be  built  fast  enough  to  take  care  of  the 
business.  By  1850,  the  time  involved  in  upstream  travel  had  been 
reduced  to  about  V18  of  what  it  had  been  before  the  appearance  of 
the  steamboat.  This  meant,  for  example,  that  the  steamboat 
brought  New  Orleans  nearly  as  close  to  St.  Paul,  for  certain  purposes, 
as  it  had  formerly  been  to  Baton  Rouge.  In  1830  the  cost  of  travel- 
ing by  water  from  New  Orleans  to  Pittsburgh  was  about  }i  what  it 


276      USES  AND   PROBLEMS  OF  INLAND   WATERS 

had  been  before  the  days  of  the  steamboat.  In  general,  the  steam^ 
boat  soon  reduced  freight  charges  to  about  y^  of  what  they  had  been, 
and  finally  to  %  and  less.  Because  of  these  things,  steamboat  navi- 
gation became  one  of  the  greatest  factors  in  the  development  of  the 
Interior. 

The  population  of  the  Interior,  commercially  dependent  for  the 
most  part  on  the  rivers,  increased  from  2^  millions  in  1S20  to  6^^ 
millions  in  1840.  Probably  no  single  factor  contributed  more  than  the 
steamboat  to  the  rapid  expansion  of  population  during  these  years. 
Thousands  settled  along  the  tributaries  of  the  Mississippi  having 
steamboat  service,  and  almost  over-night  river  towns  sprang  up  at 
favored  points.  The  total  value  of  the  commerce  of  the  western 
rivers  in  1850  was  estimated  at  $550,000,000. 

The  leading  centers  of  steamboat  trade.  During  the  period 
®f  steamboat  supremacy,  the  river  commerce  of  the  Interior  centered 
largely  in  four  cities  — •  Pittsburgh,  Cincinnati,  St.  Louis,  and  New 
Orleans. 

For  some  time  before  the  opening  of  the  Erie  Canal  (1825,  p.  286), 
Pittsburgh  was  the  eastern  gateway  to  the  Mississippi  Basin.  Im- 
portant roads  connected  it  with  the  eastern  seaboard.  Its  position 
at  the  junction  of  the  Monongahela  and  Allegheny  rivers  gave  it  many 
advantages.  The  former  brought  coal  from  West  Virginia,  while  the 
latter  gave  it  command  of  the  white  pine  of  western  New  York.  The 
principal  products  of  the  Pittsburgh  mills  reflected  these  advantages, 
together  with  the  command  of  iron  and  the  products  of  the  surround- 
ing farms.  They  were  implements  and  machinery,  iron  ware,  cabinet 
ware,  lumber,  furniture,  flour,  and  liquors.  These  things  were  sent 
by  river  throughout  the  Interior. 

Cincinnati  had  several  marked  advantages  for  the  develop- 
ment of  river  trade.  Situated  midway  on  the  Ohio  and  near  the 
northernmost  point  of  the  great  bend  of  the  river,  it  was  the  nearest 
important  river  town  for  a  large  and  fertile  region  north  of  the  Ohio, 
It  was  also  opposite  the  Licking  Valley  in  Kentucky.  The  deep 
channel  and  favorable  bank  of  the  river  along  the  city  front  made 
it  easy  to  handle  steamboat  traffic.  It  was  connected  (in  1832)  by 
canal  with  Lake  Erie  (Fig.  200).  It  received  by  river  most  of  the 
implements  and  supplies,  or  the  materials  for  their  manufacture, 
needed  by  the  tributary  farming  region.  By  river  the  city  shipped  the 
products  of  her  flour  mills,  breweries,  distilleries,  and  slaughtering 
and  packing  houses,  which  had  been  established  to  use  the  products 


LEADING  CENTERS  OF  STEAMBOAT  TRADE      277 

of  the  surrounding  country.  (Why  was  it  desirable  to  manufacture 
these  things  near  the  points  where  the  grain  and  animals  were  pro- 
duced?) These  advantages  made  Cincinnati  the  leading  city  of 
the  Ohio  Valley. 

For  years  most  of  the  capital  and  business  enterprise  of  St.  Louis 
were  engaged  in  the  river  trade,  though  later  the  city  became  an 
important  manufacturing  point.  The  following  were  the  chief  advan- 
tages which  made  it,  next  to  New  Orleans,  the  greatest  steamboat 
center  on  the  Mississippi  System,  (i)  It  is  situated  near  the  mouths 
of  the  Missouri,  Illinois,  and  Ohio  rivers.  (2)  The  Mississippi  River 
is  considerably  deeper  below  St.  Louis  than  above.  At  St.  Louis, 
therefore,  cargoes  were  exchanged  between  the  lighter-draft  boats 
of  the  river  above  and  those  of  heavier  draft  plying  on  the  river 
below. 

Because  of  its  commanding  position  near  the  mouth  of  the  Mis- 
sissippi River,  New  Orleans  had  for  years  the  greatest  commerce 
of  any  city  west  of  the  Appalachian  Mountains.  The  population  of 
New  Orleans  more  than  doubled  between  1830  and  1840,  in  spite 
of  the  growing  sand  bars  at  the  mouths  of  the  river,  frequent  inun- 
dations, and  disease  (p.  243).  No  other  important  American  city 
grew  so  fast.  But  even  before  the  Civil  War,  the  commerce  and 
growth  of  New  Orleans  had  received  several  serious  blows.  When 
canals  were  opened  between  the  Great  Lakes  and  the  Ohio,  Wabash, 
and  Illinois  rivers  (p.  286),  enormous  quantities  of  goods  from  Ohio,. 
Indiana,  Illinois,  and  even  from  parts  of  Iowa  and  Missouri,  went  to 
the  eastern  markets  by  way  of  the  Great  Lakes  and  the  Erie  Canal, 
rather  than  to  the  southern  markets.  New  Orleans  particularly  was 
injured  as  an  importing  city.  It  is  some  1500  miles  farther  than  New 
York  from  the  cities  of  northwestern  Europe,  and  the  connection  of 
New  York  with  the  Interior  by  way  of  the  Hudson  River,  Erie  Canal, 
and  Great  Lakes,  was  easier  than  that  of  New  Orleans  against  the 
current  of  the  Mississippi.  The  railroads  continued  the  work  of  the 
canals,  and  made  trade  along  east-west  lines  vastly  greater  than  that 
along  north-south  lines. 

In  addition  to  the  four  cities  mentioned,  many  smaller  cities 
and  villages  depended  largely  on  river  trade.  Such  were  Louisville, 
whose  location  was  determined  by  the  rapids  of  the  Ohio  River; 
Nashville  and  Kansas  City,  profiting  commercially  (Why?)  from  their 
respective  positions  on  the  great  bends  of  the  Cumberland  and 
Missouri  rivers;  and  Peoria,  the  leading  city  of  the  lUinois  Valley. 


278    USES  at;d  problems  of  inland  waters 

Decline  of  river  navigation.  For  years,  commerce  on  the 
Mississippi  River  and  its  tributaries  has  been  relatively  small.  The 
decline  began  at  different  times  on  different  rivers  —  for  example, 
in  1855  on  the  Illinois  River,  and  about  1883  on  the  Yazoo  River.  The 
causes  of  the  decline  also  differed  somewhat,  but  the  leading  ones  were 
of  general  application,  (i)  The  channels  of  many  of  the  rivers  were 
shallow,  crooked,  and  shifting.  (2)  The  depth  of  water  varied  much 
from  time  to  time,  and  from  place  to  place.  Boats  suited  best  to  the 
Great  Lakes  or  coastwise  trade  could  not  be  used  on  rivers  or  canals 
having  but  6  feet  of  w^ater,  and  boats  giving  the  cheapest  service  for 
6  foot  channels  could  not  be  used  in  shallower  waters,  and  so  on. 
This  was  especially  serious  because  of  the  importance  of  through 
traffic  in  American  transportation.  The  great  size  of  the  United 
States  and  the  contrasted  products  of  its  different  parts  mean  that 
much  freight  must  move  long  distances.  (3)  The  use  of  the  rivers 
forced  freight  in  many  cases  to  take  roundabout  courses.  (4)  The 
waterways  in  the  central  and  northern  parts  of  the  country  were 
closed  by  ice  a  part  of  each  year  (p.  246).  (5)  Water  transportation 
was  relatively  slow.  (6)  In  general,  the  methods,  landing  places, 
etc.,  of  river  and  canal  trade  have  remained  unimproved  since  the 
Civil  War,  and  have  been  less  and  less  able  to  meet  the  demands  of  mod- 
ern business.  (7)  When  railroads  were  built  throughout  the  Interior, 
these  disadvantages  proved  fatal  to  river  trade.  The  railroads  at 
once  got  most  of  the  passenger  trade,  and  most  of  the  traffic  in  perish- 
able and  expensive  freight.  The  rivers  could,  and  in  the  future  can, 
hope  to  compete  only  in  the  transportation  of  hea\y,  bulky,  and 
non-perishable  commodities  such  as  coal,  grain,  lumber,  building 
stone,  and  the  like.  It  is  highly  desirable  that  the  navigation  of 
the  larger  rivers  be  improved,  so  that  they  may  help  the  railroads 
in  transporting  the  ever-increasing  quantities  of  cheap  freight  (p.  287). 

Even  since  the  loss  of  most  of  their  business,  many  of  the  water- 
ways have  been  of  importance  in  regulating  railroad  freight  rates. 
Most  of  the  river  towns  that  obtained  good  railroad  connections 
did  not  suffer  greatly  from  the  decline  of  river  trade;  but  to  river 
towns  without  railroads  the  passing  of  the  steamboat  was  a  serious 
blow,  and  many  such  places  decreased  in  population. 

Present  traffic.  The  Ohio  and  its  tributaries  now  have  the 
largest  river  trade  in  the  country,  and  Pittsburgh  is  the  leading  inland 
city  in  the  volume  of  its  river  commerce.  The  traffic  is  mainly  in 
coal,  lumber,  logs,  sand,  and  gravel.     On  the  upper  Mississippi,   the 


FEATURES  OF  THE  GREAT  LAKES       279 

declining  traflSc  is  largely  in  rafted  logs  and  lumber,  and  in  sand. 
The  principal  things  transported  on  the  lower  Mississippi  are  coal, 
lumber,  crude  petroleum  (from  Louisiana),  and  plantation  products 
such  as  cotton,  sugar,  and  rice. 

In  1906,  the  total  traffic  for  the  entire  Mississippi  System,  includ- 
ing rafts  and  harbor  trafi&c,  amounted  to  only  about  30,000,000 
tons.     As  in  early  days,  most  of  the  freight  moves  downstream. 

Pacific  Rivers  of  the  United  States 
The  rivers  of  the  United  States  tributary  to  the  Pacific  Ocean 
have  a  combined  navigable  length  of  about  1,600  miles.  None  of 
them  affords  navigation  far  inland  (Fig.  191),  the  San  Joaquin  and 
Sacramento  rivers,  especially,  being  nearly  parallel  with  the  coast. 
The  Columbia  is  commercially  the  most  important  river  of  the  Pacific 
coast.  Ocean  steamships  reach  Portland  (some  miles  up  the  Willa- 
mette), no  miles  inland. 

As  the  only  river  rising  east  of  the  Cascade-Sierra  Nevada  ranges  and  directly 
tributary  to  the  Pacific  Ocean,  the  Columbia  was  the  key  to  political  expansion 
on  this  portion  of  the  coast.  The  fact  that  its  branches  approach  closely  the 
headwaters  of  the  Saskatchewan  and  Missouri  rivers,  along  which  English  and 
American  explorers  and  fur  traders  advanced,  was  sufficient  to  cause  a  dispute 
between  Great  Britain  and  the  United  States  over  the  Oregon  country. 

The  Colorado  River  is  navigable  for  light-draft  boats  in  its  lower 
course  (Fig.  191),  but  is  little  used  commercially. 

COMMERCE  OF  THE  GREAT  LAKES 

General  features  of  the  lakes.  The  Great  Lakes  are  the  most 
important  inland  waterways  in  the  world.  Their  shore-line  in  the 
United  States  is  more  than  4,300  miles  long,  if  all  the  minor  irregu- 
larities are  measured.  They  are  connected  by  canals  with  the  At- 
lantic Ocean  and  the  Mississippi  System  (Fig.  200).  Unfortunately, 
the  shores  of  the  Great  Lakes  have  few  naturally  good  harbors. 
Several  of  the  leading  cities  and  many  of  the  villages  on  them  had  their 
locations  determined  chiefly  by  the  mouths  of  creeks  or  rivers.  Thus 
Buffalo  was  located  in  part  by  the  mouth  of  Buffalo  Creek,  Cleve- 
land by  the  mouth  of  the  Cuyahoga  River,  and  Chicago  by  the  river 
of  the  same  name.  The  entrances  to  these  and  similar  streams 
were  shallow,  and  easily  choked  by  drifting  sands.  As  a  result, 
harbor  improvements  have  been  needed  frequently  throughout  the 
history  of  the  cities  concerned. 


28o      USES  AND   PROBLEMS  OF  INLAND   WATERS 

The  Great  Lakes  afford  conditions  for  transportation  in  many 
ways  vastly  superior  to  those  of  the  rivers,  and  their  commerce 
has  grown  rapidly.  The  principal  commodities  carried  on  the  Lakes 
are  iron  ore,  coal,  lumber,  and  grain  —  raw  materials  of  great  bulk, 
and  not  requiring  rapid  transportation.  In  1910,  the  total  domestic 
shipments  on  the  Great  Lakes  amounted  to  more  than  86,000,000  net 
tons,  of  which  more  than  half  was  iron  ore. 

Early  navigation.  Apart  from  their  use  by  the  Indians,  the 
Great  Lakes  were  navigated  first  by  the  French  from  eastern  Canada. 
Their  fur  traders  navigated  the  Great  Lakes  in  light  canoes  which 
could  be  used  also  on  the  streams  leading  to  and  from  the  Lakes, 
and  could  be  carried  over  the  many  portages. 


"^"^^Pbrtagesy     <^<J 


Fig.  195.    Portages  between  the  Great  Lakes  and  the  Mississippi  System. 


Most  of  the  lines  which  the  French  used  in  passing  back  and  forth  through  the 
Great  Lakes  region  (Fig.  195)  are  still  of  importance  in  trade  and  travel.  Canals 
were  cut  across  several  of  the  old  portages  (compare  Figs.  195  and  200),  and  turn- 
pikes and  railroads  followed  the  old  lines  or  ran  parallel  to  them.  A  number  of 
villages  and  cities  grew  up  at  strategic  points  where  the  French  had  built  forts  to 
guard  the  lines  of  trade.  Between  Presque  Isle  (opposite  the  city  of  Erie,  Fig.  251) 
and  the  Allegheny  River,  there  ran  at  different  times  buffalo  trail,  Indian  path,  trad- 
er's trace,  military  road,  turnpike,  and  railroad.  A  canal,  soon  abandoned,  also 
once  connected  the  city  of  Erie  with  the  Ohio  River.  Long  the  favorite  route  of 
the  French  between  the  St.  Lawrence  River  and  the  Great  Lakes,  the  Ottawa 
Valley  was  followed  by  the  Canadian  Pacific  Railroad  westward  from  Montreal, 
and  is  to  be  followed  by  the  projected  Georgian  Bay  Ship  Canal.    In  connection 


STEAM  NAVIGATION  ON   GREAT  LAKES 


281 


with  the  latter  much  water  power  will  be  made  available,  and  the  Ottawa  Valley 
probably  will  become  one  of  the  most  important  industrial  sections  of  Canada.  The 
above  facts  illustrate  the  truth  of  a  statement  that  "trade  and  civilization  in 
America  have  followed  the  arteries  made  by  geology." 

The  first  American  sailing  vessel  appeared  on  the  Great  Lakes 
in  1797,  but  for  a  time  the  number  increased  slowly.  In  18 12  some 
half-dozen  small  schooners  car-    ^^^^^^^^,^,^^^___,____^,^_^^^_,^^ 

ried  nearly  all  the  traffic  on  Lake    1 1 1 — 1„ .  .       y^i^  is'o ^  I 

Erie,  and  for  several  years  more 
the  business  of  the  upper  lakes 
was  limited  to  that  of  the  fur- 
trading  stations.  Further  devel- 
opment awaited  the  introduc- 
tion of  steam  navigation,  and 
the  settlement  of  the  neighbor- 
ing lake  and  prairie  plains. 

Steam  navigation  and  the 
settlement  of  the  Great  Lakes 
region.  Beginning  in  the  dec- 
ade 1820-1830  there  was  a  large 
movement  of  population  from 
New  England  and  New  York 
into  the  Lake  region.  For  this 
there  were  many  reasons,  one  of 
the  most  important  being  the 
great  reduction  in  the  expense 
and  time  involved  in  reaching 
the  Interior,  due  to  the  opening 
of  the  Erie  Canal  in  1825  (p.  286) 
and  the  development  of  steam 
navigation  on  the  western  Lakes 
in  the  thirties.  The  first  steamer 
appeared  on  Lake  Ontario  in 
1816,  but  not  till  ten  years  later 
did  one  enter  Lake  Michigan, 
and  not  until  1832  did  one  visit 
Chicago.     As    the    number  of 

steamboats  increased,  passenger  fares  decreased,  and  it  was  soon 
possible  to  take  household  goods,  farming  implements,  and  stock 
into  the  Interior  easily  and  cheaply. 


Fig.  197. 

Fig.  196.  Distribution  of  population 
in  the  Great  Lakes  region  in  1830. 

Fig.  197.  Distribution  of  population 
in  the  Great  Lakes  region  in  1850. 


282      USES  AND  PROBLEMS  OF  INLAND  WATERS 

A  comparison  of  Figs.  196  and  197  will  show  how  rapidly  the  nor- 
thern parts  of  Ohio,  Indiana,  and  Illinois,  and  the  southern  parts  of 
Michigan  and  Wisconsin  were  settled  between  1830  and  1850.  During 
this  period,  also,  Buffalo,  Cleveland,  Toledo,  Milwaukee,  and  Chicago 
had  their  first  substantial  growth.  They  served  as  points  of  contact 
between  the  agricultural  Interior  and  the  manufacturing  and  com- 
mercial East.  Their  prosperity  depended  on  commerce;  not  till 
later  did  they  come  to  have  large  manufacturing  interests. 

The  "  Soo  Canal "  and  the  opening  of  Lake  Superior.  Be- 
fore the  "Soo  Canal"  was  opened  in  1855  there  was  little  commerce 
on  Lake  Superior,  and  for  the  most  part  its  shores  were  an  unsettled 
wilderness.  The  canal  opened  the  borders  of  the  lake  to  settlement, 
and  permitted  the  development  of  their  natural  resources,  especially 
the  iron  ore  (p.  179)  and  lumber.  The  value  of  the  canal  was  in- 
creased greatly  in  1881,  when  the  first  enlargement  was  completed. 
Between  1880  and  189c,  the  population  of  the  Lake  Superior  counties 
of  Michigan,  Wisconsin,  and  Minnesota  increased  respectively  90 
per  cent,  400  per  cent,  and  800  per  cent.  The  canal  contributed 
greatly  to  this  remarkable  growth.  In  1896,  the  canal  was  given  a 
depth  of  20  to  21  feet,  and  a  further  enlargement  is  now  being  made. 
There  is  also  a  Canadian  canal  around  St.  Mary's  Falls. 

In  recent  years  about  ^  of  the  total  trafl&c  of  the  Great  Lakes 
has  passed  in  or  out  of  Lake  Superior  through  the  "Soo  Canal." 
The  tonnage  passing  through  it  during  the  seven  months  of  the  open 
season  is  about  four  times  as  great  as  that  passing  through  the  Suez 
Canal  during  the  entire  year.  About  V5  of  the  freight  which  passes 
through  the  "Soo  Canal"  is  east-bound. 

Traffic  in  iron  ore  and  coal.  In  recent  years  the  iron  ore  fields 
of  the  Lake  Superior  region  have  furnished  about  Vs  of  the  output 
of  iron  for  the  whole  country.  Fig.  198  shows  the  movement  of  iron 
ore  on  the  Great  Lakes.  Most  of  the  ore  goes  to  Lake  Erie  ports, 
and  thence  by  rail  to  the  Pittsburgh  region.  Most  of  the  iron  ore 
goes  to  the  coal,  rather  than  the  coal  to  the  iron,  because  the  amount 
of  coal  needed  in  manufacturing  steel  is  greater  than  the  amount 
of  iron  ore,  and  because,  where  now  manufactured,  the  steel  is  nearer 
its  market  than  it  would  be  if  manufactured  where  the  iron  is  mined. 
As  Fig.  198  shows,  much  iron  ore  also  goes  to  the  iron  and  steel  centers 
near  the  head  of  Lake  Michigan,  especially  to  South  Chicago  and 
Gary,  Indiana.  At  these  points  Indiana  and  Illinois  coal  (see  Fig.  85) 
may  be  obtained  cheaply,  and  they  are  close  to  great  markets. 


TRAFFIC  OF  THE  GREAT  LAKES 


283 


Many  boats  which  bring  iron  ore,  lumber,  and  grain  to  the  east- 
ern lake  ports  take  back  coal  at  very  low  rates.  This  has  helped 
to  make  possible  the  recent  establishment  of  the  iron  and  steel 
industry  at  the  western  end  of  Lake  Superior.     It  also  means  cheap 


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Fig.  198.  Map  showing  movement  of  iron  ore  on  the  Great  Lakes  in  1909. 
(After  Birkinbine.) 

coal  in  the  region  west  of  Lakes  Michigan  and  Superior,  which  is 
without  coal  resources  of  its  own. 

Lumber  trade  of  the  lakes.  The  western  end  of  the  great 
northern  forest  of  pine,  spruce,  hemlock,  cedar,  fir,  birch,  etc.,  lies 
in  Michigan,  Wisconsin,  and  Minnesota  (Fig.  271).  Lumbering 
began  in  Michigan  in  the  early  thirties,  and  spread  westward  and 
northward.  Production  increased  rapidly  after  1850,  and  for  many 
years  the  Lake  states  were  the  most  important  lumber  district  in  the 
United  States,  furnishing,  in  1880,  /^  of  the  total  output  of  the 
country.  Logs  cut  in  the  interior  were  floated  down  the  streams  to 
the  Lakes.    At  the  mouths  of  the  larger  rivers  busy  towns  developed 


284      USES  AND   PROBLEMS  OF  INLAND   WATERS 


where  the  logs  were  manufactured  into  lumber.  First  from  the  mill 
towns  of  eastern  Michigan,  and  later  from  more  distant  points,  the 
manufactured  lumber  was  shipped  at  low  lake  rates  to  Detroit  and 
the  cities  of  Lake  Erie.  Most  of  the  products  of  the  Lake  Michigan 
mills  were  sent  through  Chicago  to  the  prairies,  the  settlement  of 
which  created  a  demand  for  enormous  quantities  of  building  and 
fence  material.  As  the  pine  forests  near  the  Lakes  and  along  the 
larger  rivers  flowing  into  them  were  cut  away,  mill  towns  sprang 
up  in  the  interior,  from  which  more  and  more  lumber  and  lumber 


Loading  ore  at  Escanaba.     (Copyright  by  Detroit  Publishing  Co.) 


products  have  been  sent  to  market  by  rail.  This  change  and  the 
general  decline  of  the  lumber  industry  in  the  Lake  region  since 
1890  (p.  372),  due  to  the  cutting  away  of  the  forests,  have  reduced 
greatly  the  lumber  trade  of  the  Great  Lakes.  In  1910,  1,208,000 
thousand  feet  of  lumber  were  transported  on  the  Lakes. 

Movement  of  grain  and  flour.  The  transportation  of  grain 
and  flour  has  been  an  important  phase  of  commerce  on  the  Great 
Lakes  ever  since  the  settlement  of  the  Lake  states.  The  movement 
is  almost  entirely  from  the  south  end  of  Lake  Michigan  and  the 
west  end  of  Lake  Superior,  to  the  east  end  of  Lake  Erie  (Why?). 

Modem  lake  vessels.  Much  of  the  freight  on  the  Great  Lakes 
is  carried  in  steel  freighters,  built  for  speed,  capacity,  and  strength 
(Fig.  199).  Many  are  500  to  600  feet  long,  and  have  a  capacity 
of  10,000  to  12,000  tons.    One  of  the  largest  carried  13,000  tons  of 


CANAL  BUILDING  IN  THE  UNITED  STATES      285 


soft  coal  in  a  single  cargo,  and  on  another  occasion  422,000  bushels 
of  wheat.  Another  lake  vessel  transported  more  than  323,000  tons 
of  iron  ore  in  27  cargoes  during  the  season  of  1907. 

CANALS 

General  considerations.  The  first  canal  in  the  United  States 
was  opened  in  1794,  but  there  were  few  of  importance  until  the 
successful  completion  of  the  Erie  Canal  (1825)  aroused  general 
interest  in  canals.   The 


period  of  most  active 
canal  digging  extended 
from  1825  to  1837. 
Altogether,  about  4,500 
miles  of  canals  have 
been  constructed  in  the 
United  States  (Fig. 
200).  Most  of  them 
extended  and  supple- 
mented natural  water- 
ways. The  more  im- 
portant ones  were  of 
three  classes:  (i)  Those 
along  the  Atlantic 
coast,  connecting  bays 
or  rivers  between  which 
the  natural  water  routes 
involved  much  greater 
distances.  (2)  Those 
connecting,  or  begun 
with  the  intention  of 
connecting,  the  leading 
Atlantic  seaports  with  the  Ohio  River  or  the  Great  Lakes.  (3)  Those 
connecting  the  Great  Lakes  with  the  Mississippi  System.  As  Fig. 
200  shows,  many  feeders  were  built  for  the  main  canals. 

Of  the  4,500  miles  of  canals  constructed,  nearly  2,500  miles, 
costing  about  $80,000,000,  have  been  abandoned.  Most  of  the  con- 
ditions which  contributed  to  the  decline  of  river  navigation  (p.  278) 
contributed  even  more  to  the  decline  of  the  canals.  They  were  all 
shallow,  and  the  canal  boats  were  therefore  of  small  capacity; 
many  of  the  canals  varied  in  size  in  their  different  parts,  retarding 


Fig.  200.  Map  showing  principal  canals  con- 
structed in  the  United  States.  Most  of  them  are 
no  longer  used. 


286      USES  AND  PROBLEMS  OF  INLAND  WATERS 

through  traffic.  Most  of  the  canal  boats  were  towed  by  animals. 
Some  of  the  canals  were  located  unwisely,  some  were  managed  badly, 
and  most  of  them  fell  an  easy  prey  to  railroad  competition. 

The  Erie  Canal.  The  Erie  Canal,  connecting  the  Hudson 
River  with  Lake  Erie  at  Buffalo  (Fig.  200),  was  built  by  New  York 
to  control  the  trade  of  the  central  and  western  parts  of  that  state,  as 
well  as  to  gain  the  trade  of  the  Great  Lakes  region,  toward  which 
settlement  was  setting.  Some  of  the  products  of  the  former  sections 
were  going  down  the  Delaware  and  Susquehanna  rivers  to  Philadelphia 
and  Baltimore,  and  some  were  seeking  the  Canadian  markets  along  the 
St.  Lawrence  River.  Such  a  canal  was  needed  also  for  military 
reasons.  In  the  event  of  another  war  along  the  northern  frontier, 
some  way  better  than  any  existing  during  the  War  of  18 12  was  needed 
to  get  supplies  to  the  shores  of  the  Lakes. 

The  canal  became  a  great  highway  of  expansion  into  the  Inte- 
rior, and  a  great  outlet  for  surplus  western  products;  it  caused  the 
rapid  growth  of  Buffalo,  Rochester,  and  other  places  along  its  course; 
it  increased  land  values  throughout  the  region  tributary  to  it;  and  it 
helped  to  transform  New  York  City  from  a  market  town  for  the 
Hudson  Valley  into  the  leading  commercial  city  of  the  continent. 
The  cost  of  transportation  between  Albany  and  Buffalo  fell  from 
$88  to  $5.98  a  ton  in  the  twenty-six  years  after  the  opening  of  the 
canal.  The  tolls  collected  on  the  canal  paid  for  its  construction  in 
10  years. 

Until  the  late  i86o's,  the  Erie  Canal  was  the  most  important 
transportation  route  between  the  Great  Lakes  and  the  Atlantic 
Ocean.  In  1866,  the  freight  carried  by  the  canal  was  60  per  cent  of 
that  moved  across  New  York.  Soon  after  this  it  began  to  decrease, 
and  the  tonnage  on  the  canal  has  been  small  for  years.  The  people 
of  New  York  voted  in  1903  to  spend  $101,000,000  in  improving  the 
canal,  and  this  work  is  now  in  progress. 

Canals  between  Great  Lakes  and  Mississippi  System.  It  is 
impracticable  to  consider  here,  one  by  one,  the  different  canals 
which  connected  the  Great  Lakes  with  the  Ohio  and  Mississippi 
rivers  (Fig.  200).  In  general,  they  injured  the  cities  and  trade 
of  the  Mississippi  River  (p.  277),  and  benefited  greatly  the  cities  and 
commerce  of  the  Great  Lakes.  For  a  time,  most  of  them  were 
powerful  factors  in  the  development  of  the  sections  which  they 
crossed.  In  addition  to  giving  special  benefits  in  different  cases,  they 
cheapened  transportation,  opened  new  markets,  raised  the  prices  of 


IMPROVEMENT  OF  WATERWAYS  287 

farm  products,  lowered  the  cost  of  imported  merchandise,  increased 
land  values,  stimulated  the  growth  of  population,  and  helped  build 
up  towns  and  cities.  Some  of  these  canals  have  been  abandoned, 
and  for  years  the  rest  have  been  used  but  little. 

Foreign  canals.  Several  foreign  countries  have  systems  of 
canals  suited  to  modern  conditions  of  transportation.  This  is  true 
particularly  of  Germany.  One  of  the  important  canals  of  Germany 
(the  Kiel  Canal)  was  built  to  permit  ships  to  pass  between  the  Baltic 
and  North  seas  without  going  around  Denmark.  The  Manchester 
Ship  Canal  allows  ocean-going  ships  to  reach  the  docks  of  Manchester 
from  Liverpool. 

IMPROVEMENT   OF  AMERICAN  WATERWAYS 

Why  waterways  should  be  improved.  The  larger  rivers  of 
the  United  States  should  be  so  improved  as  to  make  possible  eco- 
nomical transportation  upon  them.  This  is  desirable  because  (i) 
water  transportation  is  normally  cheaper  than  rail  transportation, 
and  if  the  cost  of  transportation  is  reduced,  the  price  to  the  consumer 
of  the  things  transported  will  tend  to  be  lower;  (2)  waterways  tend  to 
keep  down  the  rates  of  competing  railroads;  and  (3)  in  recent  pros- 
perous years  the  railroads  have  been  unable  to  handle  promptly  the 
trafi&c  of  the  country  during  the  busy  season.  The  products  and 
trade  of  large  sections  of  the  country  are  increasing  much  faster  than 
the  transportation  facilities  of  the  railroads. 

Leading  improvements  needed.  Among  the  projected  improve- 
ments are:  (i)  A  deep  canal  (at  least  20  feet)  between  the  Hudson 
River  and  the  Great  Lakes.  The  new  Erie  Canal  (p.  286)  will  have  a 
depth  of  12  feet.  (2)  A  deep  inner  waterway  along  the  Atlantic  coast 
from  New  England  to  Florida,  connecting  various  bays  and  sounds. 
(3)  A  deep  waterway  between  Lake  Michigan  and  the  Gulf  of  Mexico. 
This  involves  extending  the  Chicago  Sanitary  and  Ship  Canal  (built 
primarily  to  dispose  of  the  sewage  of  Chicago)  to  the  head  of  naviga- 
tion on  the  Illinois  River,  and  improving  the  Illinois  and  Mississippi 
rivers.  Such  a  waterway  would  be  of  great  importance  to  the  trade 
between  the  northern  and  southern  parts  of  the  Interior,  and,  follow- 
ing the  opening  of  the  Panama  Canal  (p.  355),  to  the  trade  of  the 
northern  Interior  with  the  Pacific  coast,  and  with  foreign  countries 
both  to  the  south  and  across  the  Pacific  Ocean.  (4)  A  canal  to  connect 
Puget  Sound  and  the  Columbia  River. 


288      USES  AND  PROBLEMS  OF  INLAND   WATERS 


Water  Power 

Use  in  the  past  in  United  States.  Water  power  has  located  many 
manufacturing  cities  in  the  United  States,  and  contributed  largely 
to  their  growth.  It  was  used  first  in  a  large  way  in  New  England, 
where  it  is  one  of  the  leading  natural  resources.  Bellows  Falls, 
Holyoke,  Manchester,  Lowell,  Berlin,  Biddeford,  Lewiston,  Rumford 
Falls,  Augusta,  and  Bath  are  among  the  busy  industrial  centers 
created  largely  by  water  power.  There  are  also  many  water  power 
cities  farther  west.  Grand  Rapids,  Michigan,  a  leading  furniture 
manufacturing  center,  is  an  example.  Located  40  miles  inland,  at  the 
rapids  of  the  Grand  River,  its  first  lumber  mills  were  at  a  disad- 
vantage compared  with  those  on  the  shores  of  the  Lakes  (p.  283; 
Why?).  As  a  result,  cabinet  shops  and  furniture  factories  were  soon 
established.  (What  was  gained  by  doing  this?)  The  power  afforded 
by  the  river  was  soon  outgrown,  and  the  timber  supply  in  the  vicinity 
exhausted,  but  the  advantages  of  an  early  start,  and  of  established 
piants  with  world-wide  reputations  for  furniture  of  superior  quality, 
keep  the  city  to  the  front.  Similarly,  St.  Anthony's  Falls  and 
command  of  the  forests  and  wheat-fields  of  Minnesota  made  Minne- 
apolis an  important  manufacturing  city.  Nearly  Vio  of  the  flour 
and  grist  mill  products  of  the  country  are  manufactured  there. 

Water  power  formerly  had  certain  disadvantages,  because  the 
mills  using  it  had  to  be  close  to  the  source  of  the  power.  Coal  was 
abundant,  cheap,  and  easily  shipped,  and  was  used  more  and  more 
for  manufacturing  purposes.  Water  power  continued  to  be  used 
most  in  connection  with  long-established  industries,  and  in  connec- 
tion with  industries  demanding  special  conditions,  such  as  the  manu- 
facture of  paper  and  wood-pulp. 

Present  conditions  and  future  importance.  In  recent  years 
there  has  been  a  great  increase  in  the  use  of  water  power  in  the 
United  States.  In  1900,  less  than  1,500,000  horse  power  were  devel- 
oped from  water,  and  in  1908  more  than  5,350,000  horse  power. 
This  change  has  been  due  largely  to  the  following  conditions,  which 
also  will  help  to  bring  about  an  increasing  use  of  water  power  in  the 
future:  (i)  There  have  been  rapid  developments  in  the  transmission 
of  energy  in  the  form  of  electricity.  Electric  power  developed  by 
falls  and  rapids  {hydro-electric  power)  is  transmitted  some  300  miles 
by  a  Colorado  company.  On  the  basis  of  transmission  for  200  miles, 
a  water  power  could,  if  sufl&cient,  serve  an  area  of  125,000  square  miles. 


USE  AND  IMPORTANCE  OF  WATER  POWER      289 

In  the  future,  few  places  in  the  United  States  will  be  beyond  the  reach 
of  hydro-electric  power.  Power  from  Niagara  Falls  now  runs  street 
cars,  lights  buildings,  and  is  furnished  very  cheaply  for  manufacturing 
purposes  in  Buffalo  and  other  cities  as  far  away  as  Utica.  On  the 
Canadian  side,  it  is  carried  to  various  cities  and  villages  as  far  away 
as  the  Detroit  River.  Snoqualmie  Falls,  Washington,  furnish  power 
for  electric  lights,  street  railways,  motors,  etc.,  in  Seattle  and  Ta- 
coma,  some  50  miles  distant.  (2)  In  some  ways,  electric  power  is 
better  than  other  kinds  for  large  plants,  and  it  also  has  a  great  ad- 
vantage over  other  forms  of  power  in  that  it  may  be  carried  econom- 
ically to  the  small  user.  (3)  In  many  places,  hydro-electric  power  is 
even  now  cheaper  than  power  obtained  from  coal. 

It  is  estimated  that  about  3/^  of  the  power  now  developed  from  coal  in  the 
United  States  could  be  developed  cheaper  by  water.  Furthermore,  the  substitu- 
tion would  lengthen  greatly  the  duration  of  the  coal  supply  (p.  177). 

As  the  supply  of  coal  diminishes  and  its  cost  increases,  electricity 
developed  by  water  will  be  used  more  and  more  for  transportation, 
lighting  purposes,  and  manufacturing.  Doubtless  the  time  is  not 
distant  when  most  railroads,  street  cars,  and  interurban  lines  will 
be  operated  in  this  way.  In  time,  nearly  all  manufacturing  industries 
will  depend  largely  on  water  power,  and  it  is  fortunate  indeed  for  the 
future  of  the  United  States  that  its  available  water  power  is  so  great. 

Amount  and  distribution  of  water  power  in  the  United  States. 
In  view  of  the  part  which  water  power  is  to  play  in  the  life  of  the 
nation,  its  amount  and  distribution  are  matters  of  great  interest 
and  importance.  The  total  amount  has  been  estimated  on  several 
bases,  (i)  If  the  amount  of  water  available  in  the  streams  during 
the  two  weeks  of  lowest  water  were  used  throughout  the  year,  and 
if  all  above  that  amount  escaped  unused,  about  37,000,000  horse 
power  could  be  developed.  This  is  called  the  primary  horse  power. 
(2)  If  plants  were  established  to  develop  the  minimum  power  avail- 
able for  the  six  high-water  months,  there  would  be  about  66,500,000 
horse  power  per  year.  (3)  If  the  flood  waters  were  stored  in  reser- 
voirs, so  that  the  streams  were  utilized  fully,  there  could  be  developed 
between  100,000,000  and  200,000,000  horse  power.  The  meaning 
of  these  figures  is  realized  best  when  it  is  remembered  that  now 
about  26,000,000  horse  power  are  developed  from  coal,  and  only 
about  5,500,000  from  water.  The  estimated  distribution  of  water 
power  throughout  the  country  on  the  first  two  bases  given  above 
is  shown  in  the  table  on  the  next  page. 


290      USES  AND  PROBLEMS  OF  INLAND  WATERS 

ESTIMATE  OF  WATER  POWER  IN  THE  UNITED  STATES 

Horse  Power  Available 

^  .     •     ,  T^     .                                                                                          Prim-irv  or  Minimum  of 

Principal  Dramages                                                                       nSm  ^te  Six  Highest 

Months 

Northern  Atlantic  to  Cape  Henry,  Va 1,702,000  3,186,600 

Southern  Atlantic  to  Cape  Sable,  Fla 1,253,000  1,957,800 

Eastern  Gulf  of  Mexico  to  Mississippi  River 559,000  963,000 

Western  Gulf  of  Mexico,  west  of  Vermilion  River 433,760  822,650 

Mississippi  River,  main  stream 147,000  335,ooo 

Mississippi  River  tributaries  from  east 2,472,590  4,940,300 

Mississippi  River  tributaries  from  west,  including  Ver- 
milion River 3,948,970  7,085,000 

St.  Lawrence  River  to  Canadian  Line 6,682,480  8,090,060 

Colorado  River,  above  Yuma,  Ariz 2,918,500  5,546,000 

Southern  Pacific  to  Point  Bonita,  Cal 3,215,400  7,808,300 

Northern  Pacific 12,979,700  24,701,000 

Great  Basin 518,000  801,000 

Hudson  Bay 75, 800  212,600 

Total 36,906,200  66,449,310 

Improving  water  powers.  It  is  highly  desirable  that  power 
streams  should  maintain  a  relatively  even  flow.  If  a  stream  can 
develop  5,000  horse  power  during  brief  flood  stages,  and  only  500 
horse  power  the  rest  of  the  time,  not  much  more  than  the  latter 
amount  can  be  used,  and  the  rest  is  lost.  Forests  about  the  head- 
waters of  mountain  streams  and  systems  of  reservoirs  hold  back 
the  storm-waters  and  tend  to  keep  the  flow  of  streams  steady.  They 
are  therefore  important  to  manufacturing,  as  well  as  to  navigation  and 
farming  (pp.  166-169,  221-222). 

Water  power  in  other  countries.  Water  power  is  afforded 
by  most  large  streams  in  mountain  regions,  and  by  many  youthful 
streams  in  other  regions,  especially  those  that  have  been  glaciated 
recently.  In  Europe,  Switzerland  is  likely  to  be  the  first  country 
to  utilize  fully  its  large  water  power  resources.  The  streams  of 
Scandinavia,  Austria-Hungary,  France,  Italy,  and  Germany  also 
afford  much  power.  Enormous  power  could  be  developed  from  the 
streams  of  the  Caucasus  and  Himalaya  mountains,  but  this  is  not 
Hkely  to  be  done  in  the  near  future.  Considerable  power  may  be 
obtained  from  the  streams  of  eastern  Australia.  Canada  has  an 
abundance  of  water  power,  both  in  the  western  mountains  and  in 
the  eastern  part  of  the  country.  In  the  latter  section,  it  is  due 
largely  to  glaciation.  Many  other  countries  have  more  or  less 
water  power,  much  of  which  will  be  of  value  to  man  sometime,  if 
not  so  now. 


WHY  IRRIGATION  IS  PRACTICED  291 

Irrigation 

Irrigation  means  the  artificial  application  of  water  to  land  for 
the  benefit  of  plants.  It  is  practiced  in  many  dry  regions  because 
otherwise  crops  cannot  be  grown,  and  it  is  being  introduced  more 
and  more  into  humid  regions,  in  order  to  increase  the  yield  of  crops. 
Even  in  extern  United  States,  there  is  scarcely  a  year  when  some 
crops  do  not  suffer  from  lack  of  rain,  and  there  are  occasional  years 
of  serious  droughts. 

The  common  statement  that  farming  without  irrigation  cannot  be 
carried  on  successfully  where  the  annual  rainfall  is  less  than  twenty 
inches  is  very  misleading.  The  development  of  "dry  farming" 
(p.  329)  and  the  introduction  of  drought-resisting  plants  (p.  173)  are 
changing  some  semi-arid  regions  into  fairly  productive  farm  lands, 
without  irrigation.  Again,  much  depends  on  the  distribution  of  the 
rainfall.  If  it  came  just  when  the  plants  needed  it,  ten  or  twelve 
inches  would  suffice  to  grow  many  staple  crops  by  ordinary  methods 
of  farming.  The  yields  that  would  be  obtained  under  such  conditions 
could  be  increased  greatly,  however,  by  irrigation. 

Practiced  since  ancient  times.  Irrigation  was  practiced  in 
Egypt  2,000  years  before  Christ,  and  probably  much  earlier,  but  the 
area  irrigated  then  was  much  less  than  now.  About  6,000,000  acres 
have  been  irrigated  in  Egypt  in  recent  years.  The  ancient  civiliza- 
tions which  existed  in  Mesopotamia  were  made  possible  by  extensive 
systems  of  irrigation.  The  ditches  of  the  region  have  long  been 
unused,  and  much  land  which  once  was  cultivated  is  now  waste. 
The  English  government  has  extended  irrigation  in  India  until  about 
50,000,000  acres  are  so  watered. 

IRRIGATION  IN  WESTERN  UNITED   STATES 

Irrigation  was  practiced  first  in  the  United  States  in  Arizona 
and  New  Mexico.  In  the  latter,  there  are  ditches  said  to  have 
been  used  continuously  for  300  years  by  people  of  mixed  Span- 
ish and  Indian  descent.  The  Mormons  were  the  first  Americans 
(except  Indians)  to  irrigate  systematically.  The  conditions  for 
irrigation  were  ideal  on  the  slopes  of  alluvium  at  the  base  of  the 
Wasatch  Mountains,  and  without  irrigation  they  could  not  have 
been  cultivated.  Irrigation  by  Americans  in  the  Salt  River  Valley 
of  Arizona  began  in  1867,  and  in  southern  California  a  few  years 
later. 


292      USES  AND   PROBLEMS  OF  INLAND  WATERS 


Value  of  irrigated  land.  Irrigation  changes  unproductive, 
worthless,  or  nearly  worthless  land  into  land  producing  more  than 
the  average  farm  land  in  eastern  United  States.     (Compare  Figs. 


Fig.  20I.     The    Yakima    desert    before    irrigaliun.     2s car    >surl.ii    Yakima 
Washington.     (U.  S.  Reclamation  Service.) 


Fig.  202.    The  region  shown  in  Fig.  201,  after  irrigation.     (U.  S.  Reclama- 
tion Service.) 


VALUE  OF  IRRIGATED  LANDS 


293 


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201  and  202.)  Irrigated  lands  are  worth  $100  or  $150  an  acre  for 
general  farming  purposes,  and  choice  fruit  lands  with  good  orchards 
are  worth  $1 ,000  or  more  an  acre.  In  general,  the  great  value  of  much 
of  the  irrigated  land  is  due  to  the  following:  (i)  The  soil  of  arid  regions 
is  likely  to  be  rich  in  mineral  plant  foods,  because  for  ages  ground- 
waters have  come  to  the  surface  through  capillary  action,  and  as 
they  evaporated  into  the  dry  air  they  have  deposited  in  the  soil  the 
mineral  matter  dissolved 
during  their  journey  un- 
der-ground (p.  212).  In 
some  cases  when  irrigating 
waters  have  been  turned 
on  the  land  it  has  been 
found  that  so  much  of 
certain  materials  (alkaline 
salts  or  "alkali")  had  ac- 
cumulated in  this  way  in 
the  soil,  that  plants  would 
not  thrive  until  the  alkah 
was  partly  leached  out. 
(2)  Irrigated  soils,  when 
used  rightly,  are  durable, 
for  soil  wash  can  be  avoid- 
ed largely,  and  the  store 
of  soluble  mineral  matter 
in  the  sub-soil  is  large.  (3) 
Irrigating  waters  contain 
fertilizing  matter  in  solu- 
tion. (4)  Irrigated  crops, 
if  properly  cared  for,  get 
just  the  amount  of  water 
needed  at  just  the  time  they  need  it.  (5)  In  the  warmer  sections  of 
the  West,  several  crops  a  year  may  be  grown. 

Area  of  irrigable  land.  As  the  demand  for  land  increases  with  the 
population,  it  will  be  advisable  to  extend  irrigation  to  the  utmost 
limit.  It  is  estimated  that  about  45,000,000  acres  (an  area  the  size  of 
Missouri)  are  irrigable.  This  is  only  about  5  per  cent  of  the  entire  arid 
region.  The  chief  factors  which  will  control  the  area  which  can  be 
irrigated  are  matters  of  topography  and  rainfall,  (i)  The  water 
supply  comes  largely  from  rain  and  snow  falling  on  the  mountains, 


Fig.  203.  Diagram  showing  discharge  of 
the  Boise  River  above  Boise,  Idaho,  in  1895 
and  1896.     (Newell,  U.  S.  Geol.  Surv.) 


294      USES  AND   PROBLEMS  OF  INLAND   WATERS 


and  the  mountain  catchment  areas  are  comparatively  small.  Further- 
more, only  a  small  fraction  of  the  rainfall  of  the  arid  region  can  be 
made  available  for  irrigation  (Why?),  (2)  The  volume  of  many  of 
the  western  rivers  varies  greatly  (Why?  Fig.  203),  and  in  many  cases 
it  is  necessary  to  build  dams  to  hold  the  flood  waters  in  reservoirs,  so 
that  they  may  be  let  out  as  needed  during  the  growing  season.  Un- 
fortunately, there  are  comparatively  few  places  suited  for  the  storage 

of  large  amounts  of 
water,  and  in  some  cases 
where  there  are  good 
sites  for  dams,  the  areas 
tributary  to  them  furn- 
ish little  water.  (3)  In 
many  places  the  ground 
is  so  rough  that  the 
water  cannot  be  spread 
over  it  properly,  (4)  In 
many  places  the  possible 
crops  probably  would 
not  justify  the  expense 
of  getting  the  water  on 
the  land,  (5)  The  area 
which  can  be  irrigated 
depends  in  part  upon 
the  amount  of  water  per 
acre  required  for  crops. 
In  the  case  of  the  gov- 
ernment projects  (p.  295),  this  varies  from  i^  to  5^^  acre-feet^ 
per  year.  (Apart  from  the  fact  that  some  crops  require  more  water 
than  others,  why  should  the  variation  be  so  great?) 

There  are  several  reasons  for  hoping  that  the  irrigable  areas  ma> 
prove  larger  than  stated  above,  (i)  Many  fields  are  now  poorly 
prepared  for  the  water,  so  that  it  spreads  unevenly,  and  more  is 
required  than  would  be  if  the  land  were  less  uneven.  With  the 
land  better  prepared,  the  water  could  be  spread  over  a  larger  area, 
(2)  Much  more  land  could  be  watered  if  loss  by  seepage  from  the 
canals  were  not  so  great.  This  now  amounts,  on  the  average,  to  about 
25  per  cent  of  the  water.    The  loss  probably  will  be  reduced  more 

^An  acre-foot  of  water  is  the  amount  which  would  cover  an  acre  of  ground  to 
the  depth  of  one  foot. 


Fig.  204.  A  canal  lined  with  cement.  Truckee- 
Carson  Project,  Nevada.  (U.  S.  Reclamation 
Service.) 


GOVERNMENT  IRRIGATION  PROJECTS 


295 


and  more  by  lining  the  canals  with  cement  (Fig.  204).  (3)  The  loss 
of  water  by  evaporation  from  the  canals  also  will  be  reduced.  (4) 
Many  irrigators  now  use  much  more  water  than  is  necessary  to 
secure  the  largest  returns.  This  will  be  corrected  by  legislation, 
and  by  increasing  intelligence  on  the  part  of  the  farmers.  (5)  Meas- 
urements to  determine  the  amount  of  available  water  have  been  made 


Fig.  205.     Map  showing  Government  irrigation  projects. 

on  only  a  part  of  the  western  streams,  and  on  most  of  these  the 
records  cover  only  a  few  years.  Further  work  along  this  line  may 
show  that  the  streams  can  furnish  more  water  than  is  now  supposed. 
(6)  For  much  of  the  West  detailed  topographic  surveys  have  not  been 
made,  and  they  may  add  new  possibilities. 

Government  projects.  Irrigation  was  begun  in  the  West  by 
individual  settlers,  who  led  water  to  their  fields  from  small  rivers  and 
creeks  through  ditches  which  they  dug.  Co-operation  was  necessary, 
however,  before  extensive  areas  could  be  watered.  This  has  been 
brought  about  in  various  ways.  Many  so-called  "  irrigation  districts  " 
have  been  organized  to  reclaim  arid  land  under  state  laws.     Since 


296      USES  AND  PROBLEMS  OF  INLAND  WATERS 


1894,  much  land  has  been  reclaimed,  especially  in  Idaho  and 
Wyoming,  under  the  Carey  Act,  which  provides  for  irrigation 
through  co-operation  by  the  nation,  state,  corporations,  and  settlers. 
While  much  was  being  accomplished  in  these  ways,  it  became  evident 
that  the  federal  government  must  itself  undertake  those  projects 
that  were  too  expensive,  too  large,  or  too  slow  in  producing  returns, 
to  tempt  individuals  or  companies.  Hence  Congress  passed  the 
National  Reclamation  Act  in  1902.     This  act  provides  that  money 

derived  from  the  sale  of 
public  lands  in  the  arid 
states  shall  constitute  a 
reclamation  fund.  The 
cost  of  any  given  project 
is  assessed  against  the 
land  benefited,  and  is 
paid  by  the  settlers  in 
ten  equal  annual  pay- 
ments. The  moneys 
returned  to  the  govern- 
ment, together  with  the 
proceeds  of  the  sale  of 
other  lands,  are  used 
again  for  further  recla- 
mation. 

There  are  some  thirty  government  projects  under  way  (Fig.  205), 
which,  when  finished,  will  irrigate  more  than  3,000,000  acres.  The 
average  cost  to  the  settler  probably  will  be  $40.00  to  $50.00  per 
irrigated  acre.  The  success  of  these  great  projects  of  the  government 
has  stimulated  private  enterprise  greatly. 

A  few  facts  concerning  some  of  the  government  projects  will  illus- 
trate the  scope  of  the  work.  The  Salt  River  Project  (Arizona)  has 
the  recently  completed  Roosevelt  dam,  280  feet  high  and  1080  feet 
long  on  top.  This  dam  forms  a  lake  covering  16,320  acres.  The 
power  developed  by  the  water  as  it  comes  out  is  used  to  pump  ground- 
water to  irrigate  more  land,  for  lighting  purposes,  and  in  other  ways. 
The  storage  dam  for  the  Rio  Grande  Project  is  one  of  the  largest  in  the 
world.  It  will  make  a  lake  40  miles  long,  covering  40,000  acres,  and  con- 
taining 2,600,000  acre-feet  of  water.  The  water  for  the  Truckee- 
Carson  Project  (Nevada)  is  stored  in  Lake  Tahoe,  a  glacial  lake 
in  the  Sierra  Nevada  Mountains.     From  Truckee  River,  the  out- 


Fig.  206.     Site  of   the  great  dam  on  the  Sho- 
shone River,  in  Wyoming. 


PRODUCTS  OF  IRRIGATED   LANDS  297 

let  of  the  lake,  it  is  diverted  into  a  canal  and  carried  across  to  the 
Carson  Valley  to  reclaim  land  formerly  composed  largely  of  sand 
dunes  and  alkali  flats.  Nearly  half  the  area  of  the  Klamath  Project 
(California-Oregon)  is  occupied  by  swamps  and  lakes,  so  that  it 
must  be  drained  before  it  can  be  tilled.  After  being  drained,  it  will 
need  to  be  irrigated.  The  water  supply  for  the  Shoshone  Project, 
in  northern  Wyoming,  is  derived  from  the  Shoshone  River.  To 
regulate  the  flow  of  this  river,  the  government  has  built  a  dam  328^ 
feet  in  height  (Fig.  206),  the  highest  structure  of  the  kind  ever  built. 

Crops  of  the  irrigated  lands.  Many  different  crops  are  grown 
on  the  irrigated  lands,  for  the  conditions  affecting  plant  life  vary 
greatly.  Alfalfa  and  sugar  beets  are  produced  in  many  places.  Hay, 
grain,  and  vegetables  are  staple  products  in  Montana  and  Wyoming. 
In  addition  to  these  things,  fruits  are  grown  extensively  in  Idaho, 
Washington,  Oregon,  and  Colorado.  The  great  citrus  fruit  region  is 
in  southern  California,  and  the  raising  of  these  fruits  has  increased 
rapidly  in  recent  years.  In  igio-ii,  nearly  18,000,000  boxes  of  oranges 
and  lemons  were  shipped.  The  growing  of  deciduous  fruits  (peaches, 
pears,  and  the  like)  also  has  become  of  great  importance  in  California, 
as  in  various  other  sections  of  the  West.  The  shipping  of  these  fruits 
in  large  quantities  to  distant  markets  has  been  made  possible  by  the 
development  of  the  refrigerator  car,  in  which  most  of  the  shipments 
from  California  are  made.  In  the  extreme  southwest,  the  leading 
products  are  semi-tropical  fruits,  cereals,  and  alfalfa. 

Population  capacity  of  the  irrigated  lands.  The  high  value 
of  the  irrigated  lands  encourages  methods  of  tillage  which  secure 
maximum  yields  from  minimum  areas,  and,  together  with  the  difii- 
culty  of  hiring  effective  labor  in  the  West,  leads  to  small  farms.  In 
orchard  regions,  5  to  10  acre  holdings  are  common.  On  a  number 
of  the  government  projects,  the  farm  unit  has  been  fixed  at  forty  acres. 
These  things  mean  a  dense  rural  population.  The  ultimate  popula- 
tion of  the  irrigated  lands  probably  will  be  not  far  from  one  person  to 
an  acre. 

Farm  villages.  In  many  ways,  social  conditions  promise  to 
be  nearly  ideal  in  most  of  the  irrigated  districts.  The  small  farms 
will  make  it  possible  for  many  of  the  farmers  to  live  in  town,  going 
to  and  from  their  land  daily.  It  seems  probable  that  each  5,000  or 
6,000  acres  of  cultivated  land  will  support  a  farm  village,  where  the 
farmers  will  have  the  advantage  of  graded  schools,  public  libraries, 
etc.    On  a  number  of  the  government  projects,  the  Reclamation  Serv- 


298      USES  AND  PROBLEMS  OF  INLAND   WATERS 

ice  has  laid  out  town  sites  about  six  miles  apart,  and  set  aside  lots 
for  churches,  schools,  and  cemeteries.  The  town  lots  are  sold  to 
the  highest  bidders,  the  proceeds  going  to  the  Reclamation  Fund. 
Irrigation  promises  to  create  many  small  villages,  rather  than  a  few 
large  cities. 

Irrigation  and  the  National  Forests.  From  the  standpoint  of 
irrigation,  as  well  as  of  navigation  and  water  power,  it  is  highly  impor- 
tant that  the  flow  of  the  streams  be  uniform.  The  preservation 
of  forests  about  the  headwaters  of  the  streams  helps  to  bring  about  a 
more  even  flow  of  water,  and  partly  for  this  reason  the  National 
Forests  were  established  (Fig.  207).  Outside  Alaska,  these  forest 
reserves  have  an  area  (191 2)  of  about  144,000,000  acres.  They  are 
cared  for  by  the  Forestry  Bureau  of  the  Department  of  Agriculture. 

IRRIGATION   IN   THE   HUMID   STATES 

Present  situation.  Irrigation  is  practiced  in  some  of  the  humid 
states  in  growing  certain  crops.  For  example,  water  is  pumped 
from  wells  on  to  the  land  at  various  points  on  the  coastal  plain  between 
New  Jersey  and  Florida,  to  irrigate  truck  farms.  In  the  latter 
state,  irrigation  has  been  undertaken  recently  on  a  rather  large 
scale.  This  is  particularly  interesting,  since  all  parts  of  Florida 
receive  more  than  50  inches  of  rain  a  year,  and  some  parts  more 
than  60  inches.  But  much  of  the  soil  does  not  retain  moisture  well, 
evaporation  is  great,  and  the  fruit  groves  and  truck  farms  are  bene- 
fited by  watering  during  the  drier  season.  Their  products  are  so 
valuable  that  even  a  partial  crop  failure  means  heavy  losses.  Irri- 
gation is  practiced  extensively  on  the  rice-fields  of  Louisiana,  Texas, 
and  the  Carolinas. 

As  yet,  irrigation  in  the  East  is  restricted  largely  to  special  crops 
which  warrant  relatively  large  expenditures,  such  as  strawberries, 
raspberries,  blackberries  and  other  fruits,  and  certain  vegetables. 
With  these  crops,  a  small  or  imperfect  yield  because  of  drought  is 
disastrous. 

Future  importance.  It  has  been  estimated  that  the  yield 
of  every  important  crop  of  eastern  United  States  could  be  doubled 
by  irrigation.  It  is  therefore  certain  to  be  practiced  more  and  more 
in  the  future,  as  the  population  increases  and  the  demand  for  food 
grows.  As  in  the  West,  the  irrigator  can  apply  just  the  amount  of 
water  needed  at  just  the  time  required,  and  he  can  grow  many  more 
plants  on  an  acre  than  otherwise. 


THE  NATIONAL  FORESTS 


299 


300      USES  AND  PROBLEMS  OF  INLAND  WATERS 

Reclamation  of  Swamp  and  Overflowed  Lands 

WET   lands   of   the   UNITED   STATES 

The  reclamation  of  swamp  and  lake  areas  has  been  referred  to 
incidentally  in  other  connections  (pp.  171,  241,  242,  262).  The 
matter  is  summarized  briefly  here. 

Area  and  distribution.  It  is  estimated  that  the  total  area  of 
swamp  land  in  the  United  States  is  about  79,000,000  acres,  most  of 
which  can  be  reclaimed  ultimately.  Swamp  lands  occur  in  many 
states,  but  the  largest  areas  are  in  the  states  containing  (i)  the 
Atlantic  and  Gulf  coastal  plains,  (2)  the  flood-plains  of  the  Mississippi 
River  and  its  larger  tributaries,  and  (3)  the  area  covered  by  the 
last  ice-sheet.  About  half  of  all  the  area  of  swamp  land  is  in  Florida, 
Louisiana,  Mississippi,  and  Arkansas. 

Status  and  cost  of  reclamation.  It  is  estimated  that  nearly 
16,000,000  acres  have  been  drained,  mostly  in  the  northern  interior 
states.  In  most  other  parts  of  the  United  States,  the  problem  of 
draining  wet  lands  received  little  attention  until  the  last  few  years. 
This  was  due  to  the  abundance,  till  recently,  of  good  land  not  re- 
quiring drainage.  Progress  is  now  being  made  in  Florida,  Louisiana 
(p.  171),  and  other  states. 

The  cost  of  reclamation  varies  with  the  character  of  the  swamp, 
the  methods  employed,  and  the  machinery  used,  from  $3  or  so  an 
acre,  to  $30  or  more.  In  some  cases  ditches  to  carry  off  the  water 
are  all  that  is  needed,  and  the  cost  is  then  slight;  in  other  cases  tile- 
draining  is  necessary,  and  then  the  cost  depends  largely  on  the 
character  of  the  land.  Along  many  rivers  and  coasts  it  is  necessary 
to  build  dikes.  The  water  of  the  swamps  is  then  brought  to  certain 
points  by  drains  or  ditches,  and  pumped  out  over  the  dikes.  In 
many  such  cases,  rather  large  areas  are  treated  as  units,  and  improve- 
ments in  methods  and  machinery  have  reduced  the  cost  one-half 
in  the  last  15  years.  The  average  cost  of  drainage  has  been  estimated 
at  $15  an  acre.  This  is  much  less  than  the  average  cost  of  irrigating 
dry  lands  (p.  296). 

Results  of  reclamation,  (i)  The  soils  of  most  reclaimed  swamp 
lands  are  very  fertile.  Since  most  swamp  areas  are  of  little  use,  it  is 
clear  that  drainage  greatly  increases  their  value. 

The  value  of  drained  farming  land  varies  from  $20  or  less  an  acre,  to  $500 
and  more.  It  depends  largely  on  the  character  of  the  soil,  the  climate,  transpor- 
tation facilities,  nearness  to  or  distance  from  good  markets,  etc.     It  has  been 


RECLAMATION  OF  WET  LANDS  301 

estimated  that,  when  drained,  the  swamp  lands  of  the  United  States  will  have  an 
average  value  of  $60  an  acre.     Their  present  value  has  been  estimated  at  $8  an  acre. 

(2)  The  products  of  the  drained  lands  will  increase  greatly  the 
crops  of  the  country,  and  will  feed  and  support  millions  of  people. 

(3)  An  immediate  effect  of  the  systematic  draining  of  the  swamp 
lands  will  be  to  increase  the  healthfulness  of  the  areas  concerned. 
The  principal  breeding  places  of  malaria-carrying  mosquitoes  will 
be  destroyed,  and  that  disease  practically  stamped  out.  The  present 
annual  loss  to  the  country  from  malaria,  due  to  the  reduced  efficiency 
of  the  sufferers,  the  losses  to  business  in  the  areas  affected,  etc.,  has 
been  estimated  at  $100,000,000. 

Reclamation  of  lake-covered  lands.  Swamps  merge  into  lakes, 
and  many  so-called  lakes  doubtless  are  included  in  the  estimate  of 
swamp  areas  already  given.  Ultimately,  most  shallow  ponds  and 
lakes  will  be  drained.  It  will  always  be  impracticable  to  drain  some 
lakes,  and  many  others  will  be  carefully  protected  and  preserved 
(p.  264). 

WET  LANDS  OF  OTHER  COUNTRIES 

Large  areas  of  wet  land  have  been  reclaimed  in  Europe.  Much 
land  now  farmed  in  Holland  was  won  from  the  sea.  About  ^  of 
England  was  marsh  or  bog  land  in  the  reign  of  Alfred  the  Great  (871- 
901).  Probably  "not  far  from  V2oof  the  tillable  land  in  Europe  was 
inundated  and  unfit  for  agriculture  in  the  eighth  century  of  our  era." 

Vast  areas  of  swamp  land  in  various  tropical  countries  probably 
will  remain  in  their  present  condition  for  a  long  time. 

Water  Supply 

Apart  from  its  support  of  plant  and  animal  life,  the  most  impor- 
tant use  of  water  is  for  home  and  city  purposes  —  that  is  for  drink- 
ing, bathing,  and  various  household  purposes,  for  sprinkling  streets, 
flushing  sewers,  for  fire  protection,  manufacturing,  and  the  like.  It 
is  estimated  that  between  50  and  150  gallons  of  water  per  person  are 
used  daily  in  the  cities  of  the  United  States.  Of  this,  about  half 
a  gallon  per  person  is  used  for  drinking. 

Sources  of  water  supply,  (i)  Rain-water,  stored  in  cisterns 
and  "tanks,"  is  used  extensively  for  drinking  in  the  arid  states,  and 
for  other  purposes  throughout  much  of  the  country.  (2)  Most  of 
the  country  people  of  the  United  States  obtain  water  for  domestic 
purposes  from  underground,  through  ordinary  wells  and  springs;  but 


302       USES  AND   PROBLEMS  OF  INLAND   WATERS 

no  large  city  could  get  water  enough  in  this  way.  Thousands  of 
wells  and  springs  have  failed  in  recent  years  because  the  water  table 
(p.  205)  has  been  lowered  by  unwise  farming  and  deforestation  (p.  208). 
(3)  In  the  Atlantic  Coastal  Plain,  the  Great  Plains,  and  some  other 
parts  of  the  country  where  the  arrangement  and  position  of  the 
rock  strata  are  favorable,  artesian  wells  (p.  209)  supply  large  amounts 
of  water. 

Sand  and  gravel  are  in  general  good  water  bearers,  while  clay  yields  relatively 
little  water  (Why?).  Many  wells  sunk  in  the  glacial  clays  of  northern  United 
States  obtain  their  water  chiefly  from  beds  or  pockets  of  sand  and  gravel  in  the  drift. 
Among  the  solid  rocks,  sandstone  is  a  good  water  carrier,  because  it  is  porous,  and 
shale  a  poor  one,  because  it  is  compact.  Granite  and  many  similar  rocks  are 
dense,  and  hold  little  water,  the  largest  supplies  being  found  in  cracks  and  other 
openings  in  the  rocks. 

(4)  Thousands  of  lakes,  particularly  in  the  glaciated  parts  of  the 
country,  may  serve  as  sources  of  water  supply  for  neighboring  cities 
and  villages,  and  many  are  so  used  now.  From  the  Great  Lakes  or 
their  connecting  rivers,  Buffalo,  Cleveland,  Detroit,  Milwaukee, 
Chicago,  Duluth,  and  many  smaller  cities  get  their  supply  of  water. 
(5)  Many  villages  and  cities  get  their  water  from  streams.  Thus 
New  York  City's  supply  is  from  streams  and  reservoirs  in  the  Catskill 
Mountains  and  the  uplands  east  of  the  lower  Hudson  River;  Phila- 
delphia depends  on  the  Delaware  and  Schuylkill  rivers,  Cincinnati  on 
the  Ohio,  Minneapolis  and  St.  Louis  on  the  Mississippi,  and  Omaha 
and  Kansas  City  on  the  Missouri. 

In  recent  years  various  cities  have  outgrown  their  supplies  of  water  and  have 
had  to  seek  new  supplies,  in  some  cases  at  considerable  distances  and  at  great 
expense.  Los  Angeles  is  expending  more  than  $25,000,000  in  this  way.  Water 
is  to  be  brought  from  Owens  River,  across  the  Mojave  Desert  and  through  the  San 
Bernardino  Mountains,  in  an  aqueduct  of  steel  and  concrete  some  240  miles  long. 
New  York  City  is  expending  nearly  $100,000,000  to  obtain  an  additional  supply  of 
500,000,000  gallons  a  day  from  the  Catskill  Mountains,  more  than  80  miles  away. 

Quality  of  waters.  Drinking  water  should  be  reasonably 
clear,  tasteless,  and  free  from  germs  of  disease.  Some  cities  have 
expended  large  sums  to  guard  the  purity  of  their  water.  Some 
of  them  have  bought  large  tracts  of  land,  with  their  lakes,  springs, 
and  other  stream  sources.  The  waters  of  these  tracts  are  then 
protected  carefully  from  contamination,  and  carried  to  the  cities  in 
ways  that  prevent  pollution  on  the  way.  Other  cities  have  estab- 
lished filtering  plants  through  which  all  the  city  water  passes  before 


WATER  SUPPLY  PROBLEMS  303 

use.  Nevertheless,  the  use  of  impure  drinking  water  is  still  a  leading 
cause  of  disease  in  the  United  States.  Many  wells  receive  drainage 
from  barnyards  and  cesspools  (p.  207),  many  springs  used  as  a  source 
of  drinking  water  are  exposed  to  surface  wash  and  to  pollution  by 
stock,  and  many  villages  and  cities  use  river  and  lake  water  con- 
taminated by  sewage. 

For  many  industrial  purposes,  the  value  of  water  depends  on 
the  kind  and  amount  of  mineral  matter  it  contains.  Distilleries 
and  breweries  require  water  of  exceptional  purity.  Laundries  and 
textile  mills  need  water  which  is  clear,  free  from  iron,  and  contains 
little  other  mineral  matter.  Railroad  companies  spend  large  sums 
in  treating  the  waters  used  in  their  engines,  so  as  to  make  them 
less  injurious  to  the  boilers.  Knowledge  of  the  quality  of  the  waters 
of  the  country  is  so  important  for  various  reasons  that  extensive 
investigations  of  surface  and  ground  waters  are  being  made  by  the 
United  States  Geological  Survey,  and  by  various  state  and  private 
agencies. 

Questions 

1 .  Are  cities  more  likely  to  develop  on  the  inside  or  outside  of  great  bends  on 
navigable  rivers?     Give  examples  and  reasons. 

2.  Why  does  the  cost  per  ton  for  transportation  by  water  tend  to  decrease 
as  the  size  of  the  cargo  increases? 

3.  Why  are  four- fifths  of  the  population  of  New  York  state  in  the  coimties 
bordering  the  Hudson  Eiver  and  Erie  Canal? 

4.  (i)  Account  for  the  enormous  amount  of  water  power  available  in  the 
Northern  Pacific  district,  according  to  the  table  on  page  290.  (2)  Why  do  the 
western  tributaries  of  the  Mississippi  River  afford  more  power  than  the  eastern 
tributaries?  (3)  Why  does  the  Northern  Atlantic  district  (p.  290)  furnish  more 
water  power  than  the  Southern  Atlantic? 

5.  Explain  the  fact  that  apples  and  other  fruits  are  grown  in  great  perfection 
and  abundance  on  irrigated  lands  around  Grand  Junction,  in  western  Colorado, 
while  in  the  same  latitude  in  western  Nevada  attention  is  given  largely  to  hardier 
crops,  such  as  grain  and  potatoes. 

6.  Account  for  the  fact  that  legislation  concerning  the  utilization  of  stream 
and  ground  waters  is  more  advanced  in  western  than  in  eastern  United  States. 


CHAPTER  XVII 


MOUNTAINS  AND   PLATEAUS  AND  THEIR   RELATIONS  TO 

LIFE 

Mountains  and  plateaus  have  been  referred  to  frequently  in 
earlier  pages.  The  more  important  points  concerning  their  origin, 
their  history,  and  their  relations  to  human  affairs  are  considered 
-^n  this  chapter. 

Mountains 

Distribution  of  mountains.  As  already  noted,  mountain  ranges 
are  situated  in  general  toward  the  borders,  rather  than  in  the  interiors, 
of  the  continents,  and  most  of  the  longer  and  higher  systems  are  not 
far  from  the  edges  of  the  greatest  ocean  basin.  The  settling  of  the 
ocean  basins,  due  to  the  shrinking  (partly  through  cooling)  of  the 
earth,  may  have  been  an  important  cause  of  the  uphfts  which  have 
made  mountains  near  the  edges  of  the  continents. 

Leading  types  of  mountains,  (i)  Fig.  208  shows  several  moun- 
tain ridges  of  one  type,  and  suggests  their  origin.     A  plateau  or  plain 

was  divided  by  giant  cracks 
into  a  series  of  great  blocks, 
which  were  displaced  (faulted), 
the  relatively  elevated  edges 
forming  mountain  ridges.  The 
mountain  ridges  may  be  due  to 
uplift,  or  to  the  sinking  of  the 
lower  land  adjacent  to  them, 
or  to  both.  Such  mountains 
are  called  faulted  or  block  mountains.  Block  mountains  in  various 
stages  of  dissection  occur  in  Oregon,  Nevada,  and  elsewhere. 

(2)  Mountains  consisting  of  a  series  of  folds  formed  by  com- 
pression from  the  sides  are  a  common  type.  In  some  cases  the  folds 
are  open  and  regular  (Fig.  209) ;  in  others  they  are  closed,  irregular, 
and  overturned.     In  some  cases  the  strata  of  the  folds  are  faulted 

304 


Fig.  208.     Diagram  of  block  moun- 
tains.    (Modified  after  Davis.) 


LEADING   TYPES  OF  MOUNTAINS 


305 


(Fig.  210),  and  some  of  the  faults  record  a  vertical  displacement  of 
thousands  of  feet.  The  present  topography  of  most  folded  moun- 
tains— for  example,  of  the  Appalachians  and  Juras — is  controlled  not 


Fig.  209.  Open,  symmetrical  folds  in  the  Appalachian  Moimtains.  North- 
eastern West  Virginia.  Length  of  section,  about  i2>^  miles.  The  formation 
shown  in  solid  black  contains  coal.     (After  U.  S.  Geol.  Surv.) 

so  much  by  the  original  folding  and  faulting  as  by  later  erosion 
and  warping. 

(3)  Many  of  the  higher  isolated  mountains  are  volcanic  cones 
(p.  193;  Fig.  99).     Many  mountains  have  been  formed  also  by  great 


Fig.  210.    Folded  and  faulted  strata  in  the  Appalachian  Mountains  neai 
Bristol,  Virginia.     (After  U.  S.  Geol.  Surv.) 

intrusions  of  lava  which  have  domed  or  lifted  the  overl3dng  beds  high 
above  the  level  of  the  surrounding  country  (Fig.  105).  In  many  such 
cases  the  rocks  which  covered  the  lava  have  been  partly  removed 
by  erosion,  exposing  the  core  of  intruded  rocks  (Fig.  211).     Among 

the  mountains  produced  chiefly  ^ 

by  vulcanism  and  later  erosion 
are  the  Henry  Mountains  of 
Utah,  and  the  Park  and  Elk 
ranges  (Fig.  212)  of  Colo- 
rado. 

(4)  Many  mountains  owe 
their  existence  simply  to  the 
resistance  of  their  rocks,  which 
have  been  left  standing  in  bold 
relief  by  the  removal  of  the  sur- 
rounding weaker  rocks.  Many 
mountain  peaks,  aside  from  vol- 
canic peaks,  are  of  this  origin.  pig.  212.  Cross-section  of  Elk  Moun- 
Pike  's    Peak,    Colorado,    is    a     tains,  Colorado. 


Fig.  211.  An  eroded  laccolith.  Cross- 
section  of  Mount  Killers,  Utah,  with  ideal 
representation  of  the  underground  struc- 
ture. Compare  with  Fig.  105.  (After 
Gilbert,  U.  S.  Geol.  Surv.) 


3o6 


MOUNTAINS,  PLATEAUS,  AND  LIFE 


well-known  example.  The  Catskill  Mountains  of  southeastern  New 
York  are  due  to  unequal  erosion,  where  the  resistance  of  the  rock 
is  not  very  unequal.  They  are  really  a  dissected  plateau.  Various 
other  maturely  dissected  plateaus  of  considerable  relief  are  called 
mountains. 

(5)  Folding  and  faulting,  vulcanism  and  unequal  erosion  all 
may  be  involved  in  the  formation  of  lofty  mountains.  Many  moun- 
tains, furthermore,  have  had  several  periods  of  growth,  between 
which  the  upraised  beds  suffered  great  erosion  (Fig.  213). 

The  formation  of  mountains  is  a  very  slow  process,  probably 
occupying,  for  the  greater  ranges,  hundreds  of  thousands  or  even 


Fig.  213.  Diagram  showing  structure  of  the  beds  in  the  region  of  the  Santa 
Lucia  Range,  California.  Length  of  section,  about  11  miles.  (After  U.  S.  Geol. 
Surv.) 

millions  of  years.  Many  mountains  appear  to  be  growing  now  — 
for  example,  the  St.  Elias  Range  of  Alaska. 

Destruction  of  mountains.  All  mountains  are  destroyed  in  time 
by  erosion,  unless  renewed  by  vulcanism  or  uplift.  Furthermore, 
the  erosion  of  mountains  commences  as  soon  as  they  begin  to  rise,  and 
continues  throughout  the  long  period  of  their  growth,  as  well  as  after- 
wards. As  a  result,  no  mountain  due  to  vulcanism  or  diastrophism 
(crustal  movements)  ever  had  the  full  height  which  those  processes 
would  have  given  it,  if  there  had  been  no  erosion.  As  already 
pointed  out,  many  mountains  have  been  nearly  or  wholly  removed 
by  erosion,  and  revived  again  by  uplift,  and  some  of  them  have 
passed  through  this  history  several  times.  The  length  of  the  life 
of  a  mountain  which  has  ceased  to  grow  is  determined  largely  by 
its  height,  by  the  resistance  of  its  rocks,  and  by  the  character  of  the 
climate. 

The  gentle  slopes  of  the  later  life  of  a  mountain  are  worn  less 
rapidly  than  the  steeper  slopes  of  its  earlier  career,  so  that  its  old  age 
may  be  longer  than  its  youth  and  maturity  combined.  All  lofty 
mountains  are  rather  young,  geologically  speaking;  old  mountains 
have  been  worn  low.  While  very  old  mountains  are  low,  obviously 
not  all  low  mountains  are  old. 


MOUNTAINS  AS   BARRIERS 


3^7 


Mountains  as  barriers.  Mountains  are  barriers  to  the  move- 
ment of  animals  and  men,  and  to  the  spread  of  plants  (Fig.  214). 
The  effectiveness  of  a  mountain  barrier  depends  largely  on  its  height, 
length,  and  width;  on  the  number,  height,  and  distribution  of  the 


Fig.  214.     Toltec  Gorge,  in  the  mountains  of  Colorado.     Travel  even  along 
the  valley  is  difiicult.     (Denver  and  Rio  Grande  Railroad  Company.) 


passes;  and  on  the  number  of  ridges,  and  the  steepness  and  character 
of  their  slopes.  The  high,  massive  ranges  of  the  Pyrenees,  Caucasus, 
and  Andes  mountains  form  very  effective  barriers.  The  Pyrenees 
make  the  best  natural  inland  boundary  in  Europe,  shutting  off  Spain 
so  completely  from  the  rest  of  the  continent  that  it  has  been  said: 
"Africa  begins  at  the  Pyrenees."     Although  high,  the  Alps  Moun- 


3o8 


MOUNTAINS,  PLATEAUS,  AND   LIFE 


tains  have  several  good  passes,  well  distributed;  accordingly,  they 
form  a  less  serious  barrier.  The  effect  of  many  mountain  barriers 
has  been  lessened  by  the  building  of  wagon  roads  and  railroads, 
the  cutting  of  tunnels,  etc.  In  other  cases,  mountains  are  crossed 
only  by  a  few  difficult  trails,  along  which  wares  are  taken  on  pack 
animals  or  by  human  carriers. 

For  a  long  time,  northern  and  central  Europe  was  excluded  by  mountains 
from  the  culture  of  the  leading  Mediterranean  countries.  China  is  largely  shut 
off  from  the  rest  of  Asia  by  mountains,  a  fact  of  much  i-mportance  in  connection 
with  the  isolated  development  and  backward  state  of  that  country.  The  Appa- 
lachian barrier  helped  to  confine  the  English  colonies  to  the  Atlantic  seaboard  for  a 
century  and  a  half.  This  favored  the  development  of  compact  settlements,  and 
permitted  much  more  rapid  progress  along  many  lines  than  would  have  been 


Fig.  215.     Map  showing  course  of  Cumberland  National  Road. 

possible  had  the  colonists  spread  themselves  thinly  over  a  vast  area,  after  the 
manner  of  the  French,  who  controlled  the  St.  Lawrence  gateway  into  the  Interior. 
For  years  after  the  Revolutionary  War,  the  Appalachian  Mountains  made  commu- 
nication difficult  between  the  settlements  of  the  Interior  and  the  seaboard.  The 
first  great  step  in  their  conquest  as  barriers  to  trade  and  travel  was  taken  when  the 
Cumberland  National  Road  was  completed  from  Cumberland,  Maryland,  to  the 
Ohio  River  at  Wheeling,  in  181 7  (Fig.  215);  the  second  when  the  Erie  Canal  was 
opened  (1825).  Though  this  canal  did  not  cross  the  Appalachians,  it  afforded  an 
easy  route  to  the  Interior.  The  third  and  greatest  step  in  the  conquest  of  the 
mountains  was  taken  when  four  railroads  were  finished  across  them  in  the  iSso's. 
These  first  trans-Appalachian  railroads  crossed  the  barrier  at  the  north,  where  it  is 
narrowest,  lowest,  and  has  most  good  passes.  Until  the  completion  of  the  first 
transcontinental  railroad  (1869),  travel  across  the  western  mountains  and  plateaus 
was  so  difficult  that  many  people  going  to  California  chose  the  13,000-mile  voyage 
around  Cape  Horn,  or  the  route  by  way  of  Panama. 

The  difificulty  of  crossing  high,  rugged  mountains  gives  great 
importance  to  notches  or  passes  in  their  ridges.  Many  mountain 
passes  are  water-gaps  or  wind-gaps;  their  formation  has-been  ex- 
plained, and  their  relation  to  human  affairs  illustrated  (pp.  232,  234). 


IMPORTANCE  OF  MOUNTAIN  PASSES 


309 


Trails,  wagon  roads,  and  railroads  all  seek  the  lowest  and  most  acces- 
sible passes  (Fig.  216).  They  commonly  enter  the  mountains  along 
main  valleys,  and,  where  necessary,  zigzag  up  the  steeper  slopes  to  the 
passes  which  serve  as  gateways  through  the  central  ridges  (Fig.  217). 
In  some  cases,  railroad  companies  have  avoided  the  last  part  of  the 
ascent  by  tunneling  the 


mountam 
pass. 


below    the 


South  Pass,  in  central 
Wyoming,  is  the  most  im- 
portant pass,  historically, 
in  the  Rocky  Mountains. 
Through  it  ran  the  famous 
Oregon  Trail,  along  which 
many  thousands  journeyed 
to  the  grain  lands  of  Oregon 
and  the  gold  fields  of  Cali- 
fornia. Truckee  Pass  af- 
fords a  relatively  easy  route 
across  the  central  part  of 
the  Sierra  Nevada  Moun- 
tains. It  was  used  first  by 
the  California  Trail,  and  is 
used  now  by  the  Southern 
Pacific  Railroad.  The  Pass 
of  Belfort,  between  the 
Vosges  and  Jura  mountains, 
connects  the  Rhone  and 
Rhine  valleys,  and  with 
them  has  constituted  since 
ancient  times  one  of  the 
most  important  routes   of 

travel  between  the  Mediterranean  and  North  seas.  The  passes  in  the  moimtains 
of  northwestern  India  have  served  repeatedly  as  gateways  through  which  tribes 
and  armies  from  central  Asia  have  descended  to  plunder  and  conquer  the  people  of 
the  plains. 

The  difficulties  of  travel  and  communication  in  rugged  moun- 
tains shut  their  inhabitants  away  from  the  outer  world,  helping 
to  retard  progress.  Old  customs,  fashions,  and  manners  of  speech 
are  likely  to  be  preserved  by  mountaineers  long  after  they  have 
been  abandoned  elsewhere.  Education  is  backward;  much  of  the 
simple  clothing,  furniture,  etc.,  is  home-made;  trade  in  many  cases 
is  limited  to  barter,  involving  only  the  absolute  essentials  of  life;  and 
social  intercourse  is  restricted  seriously,  favoring  the  close  intermar- 


Fig.  216.  Sketch-map  of  region  about  Holli* 
daysburg,  Pennsylvania,  showing  the  influence  ol 
mountain  passes  upon  the  course  of  wagon  roads 
and  railroads.  (From  Hollidaysburg  Sheet,  U.  S. 
Geol.  Surv.) 


3IO 


MOUNTAINS,  PLATEAUS,  AND   LIFE 


riage  of  families  and  the  development  of  "clans."    These  conditions 
are  illustrated  among  the  mountaineers  of  the  southern  Appalachians 


^^                Jtt^^^     _.^  ...^ 

C"^^^^ 

JI^"      ^^"H^^^^ 

Fig.  217.     Road  zigzagging  up  mountain  slope  in  Switzerland.    Rhone  Glacier 
in  middle  background. 

(Fig.  218).    They  do  not  exist,  of  course,  in  new  mountain  commu- 
nities established  by  progressive  people  from  outside,  and  they  have 


Fig.  218.     Homes  of  mountaineers  in  the  southern  Appalachians. 

been  changed  greatly  in  some  long-settled  mountains  (e.  g.,  in  the 
Alps)  by  the  coming  of  summer  visitors  (p.  317),  and  in  other  ways. 


THE  SETTLEMENT  OF   MOUNTAINS  .311 

Many  mountains  are  important  climatic  barriers  (p.  77),  and 
the  conditions  of  life  on  their  opposite  sides  may  be  very  different. 
The  western  slopes  of  the  Sierra  Nevada  Mountains  receive  much 
rain;  to  the  eastward  stretch  broad  deserts.  Because  most  of  its 
early  mines  proved  disappointing,  and  lack  of  rain  prevented  ordinary 
farming  in  most  places,  the  population  of  Nevada  was  always  small 
(only  42,000  in  1900).  This  was  the  penalty  of  its  position  to  the 
leeward  of  high,  rain-catching  mountains.  Recently  the  population 
of  Nevada  has  increased  (p.  330)  because  of  irrigation  and  the  dis- 
covery of  new  mineral  wealth.  The  contrast  is  even  greater  between 
the  two  sides  of  the  Himalaya  Mountains;  to  the  south  are  the 
crowded  millions  of  India,  to  the  north  the  scattered,  nomadic  tribes 
of  Tibet.  The  difference  here  is  not  due  wholly  to  the  mountains, 
but  largely  to  the  great  altitude  of  the  plateau  on  the  northern  side. 

The  settlement  of  mountains.  In  general,  the  settlement  of 
rugged  mountains  begins  only  after  the  more  in\dting  neighboring 
lowlands  have  been  occupied,  and  their  populations  are  always  rela- 
tively sparse.  The  areas  of  the  Adirondack,  Catskill,  Alleghany, 
and  other  mountains  in  eastern  United  States  were  blank  spaces  on 
the  earlier  census  maps  (Figs.  276  and  278),  and  their  populations 
are  in  most  sections  sparse  even  now  (Fig.  281).  A  similar  situation 
exists  in  the  western  mountains. 

Mountain  areas  are  settled  first  and  most  thickly  in  their  larger 

valleys.     Here  the  flatter  land  favors  tillage,  soils  are  thicker  and 

in  most  cases  more  fertile  (Why?),  the  climate  is  milder,  and  the 

trails  of  the  upland  are  replaced  by  roads. 

The  inhabitants  of  many  mountain  valleys  in  Europe  and  Asia  are  descendants 
of  people  who  sought  refuge  there  from  their  enemies.  The  Basques,  who  dwell 
in  the  western  valleys  of  the  Pyrenees,  are  an  example.  In  other  cases,  the  occupa- 
tion of  mountain  strongholds  has  permitted  people  to  dominate  the  adjoining 
lowlands,  and  levy  tribute  on  their  inhabitants.  At  the  beginning  of  the  Revolu- 
tionary War,  four-fifths  of  the  Cherokee  Indians  dwelt  within  the  southern  Appa- 
lachians, and  from  their  mountain  villages  they  repeatedly  made  sudden  attacks 
on  the  frontier  outposts  of  the  whites. 

Agriculture  in  mountains.  Outside  the  valley  bottoms,  con- 
ditions are  unfavorable  to  agriculture  in  high  mountains,  and  in 
many  places  prevent  it.  Many  slopes  are  too  steep  to  be  tilled, 
consisting  either  of  bare  rock  or  having  here  and  there  a  thin  covering 
of  soil  which  washes  easily  when  cultivated;  and  with  increasing 
height,  the  climate  prevents  the  raising  of  crops  and  even  the  growth 
of  trees  and  grasses.      Switzerland  is  largely  mountainous,  and  only 


312 


MOUNTAINS,  PLATEAUS,  AND  LIFE 


about  V6  of  its  area  is  arable  land.  Only  V7  of  the  three  Alpine  prov- 
inces of  Austria  is  tillable.  Less  than  V6  of  Japan  can  be  cultivated 
readily.  Such  conditions  mean  a  scanty  food  supply  and  a  constant 
tendency  toward  over-population.  They  mean  also  that  in  many 
long-settled  mountain  regions  the  cultivable  land  is  farmed  intensively 


Fig.  219.     Terraces  made  by  Ifugao  Igorots,  island  of  Luzon,  Philippine 
Islands. 


in  small  holdings.     Every  effort  is  made  to  maintain  the  fertility  of 
the  soil,  so  that  it  may  grow  good  crops  continuously. 

In  many  mountain  regions,  where  all  the  level  land  has  long  been 
used,  the  slopes,  too  steep  for  agriculture  by  ordinary  methods,  have 
been  utilized  by  making  terraces  (Fig.  219).  Low  walls  are  built  one 
above  another  on  the  slopes,  and  the  spaces  behind  filled  in  and  cov- 
ered with  soil.  In  this  way,  successive  tiers  of  nearly  level  benches  of 
land  (terraces)  are  made.  Terrace  agriculture  is  practiced  in  parts  of 
India,  China,  Italy,  Germany,  France,  Switzerland,  and  other  coun- 
tries.    In  Europe,  much  terraced  land  is  used  for  vineyards.     Choice 


FARMING  IN  MOUNTAINS 


313 


fields  with  bearing  vines  equal  in  price  the  best  irrigated  fruit  lands  of 
western  United  States  (p.  175). 

The  crops  which  may  be  grown  in  mountains  vary  with  the  expo- 
sure, the  altitude,  the  rainfall,  the  character  of  the  soil,  etc.  In 
general,  the  slopes  of  a  lofty  mountain  present  successive  climatic 
zones  to  which  plant  life,  and  animal  and  human  life  as  well,  are 
adjusted.     If  such  a  mountain  is  in  low  latitudes,  its  slopes  may  afford 


M 

Ki:.  •  ^rttv^^^^-:^ 

Fig.  220.     Sheep  grazing  on  a  mountain  side  in  Holy  Cross  National  Forest, 
Colorado.     (U.  S.  Forest  Service.) 

conditions  ranging  from  those  of  the  tropics  to  those  of  the  polar 
zones  (p.  22).  In  the  Alps,  the  following  changes  may  be  noted:  (i) 
In  suitable  places  on  the  sides  of  the  lower  valleys  there  are  vineyards, 
olive  orchards,  and  mulberry  groves  worked  intensively  by  a  relative- 
ly dense  population.  (2)  Higher  up,  these  are  replaced  by  grain  fields 
and  pasture  lands,  among  which  there  are  forests  of  deciduous  trees. 
This  zone  is  less  productive  and  settled  less  thickly  than  the  first. 
(3)  Still  higher,  hardy  evergreen  trees  prevail,  the  proportion  of  useless 
land  increases,  only  the  hardiest  grains  are  grown  (up  to  about  5,300 
feet)  in  small  fields  by  the  sparse  population,  and  most  of  the 
land  with  soil  is  devoted  to  pasturage  and  to  the  growing  of  hay  for 
the  winter  feeding  of  the  stock.  (4)  Above  the  "tree-line"  (the  upper 
limit  of  tree  growth  is  about  7,600  feet)  is  a  belt  in  which  some  of  the 
slopes  bear  grass,  where  cows,  sheep,  and  goats  are  pastured  for  a 


314 


MOUNTAINS,  PLATEAUS,  AND  LIFE 


short  time  in  summer.     (5)  Finally,  there  is  a  waste  of  bare,  rocky 
slopes  and  snow-fields,  unoccupied  by  life  which  is  useful  to  man. 

Stock-raising  in  mountains.  Stock-raising  is  an  important 
industry  in  many  mountains,  for  slopes  too  steep  or  too  rocky  to  be 
tilled,  or  too  high  for  cultivated  crops  to  ripen,  may  afford  pasturage 
(Fig.  220).  As  suggested  above,  pasturing  stock  and  growing  feed 
for  its  use  in  winter  constitute  a  leading  industry  in  the  higher  Alps. 
More  than  half  the  productive  area  of  Switzerland  consists  of  pasture 


Fig.  221.     Summer  grazing  in  the  High  Alps. 

land  and  hay  land.  In  spring,  herdsmen  take  their  cattle,  goats,  and 
sheep  from  the  villages  in  the  valleys  up  to  the  high  pastures,  advanc- 
ing, as  the  growth  of  the  grass  permits,  close  to  the  snow-line  (Fig. 
221),  where  the  grazing  season  may  last  only  six  or  seven  weeks.  In 
autumn,  the  flocks  and  herds  are  driven  back  by  stages  to  the  lower 
valleys,  where  they  are  fed  in  stables  during  the  long  winter.  Rais- 
ing enough  hay  and  other  fodder  for  the  winter  feeding  is  perhaps 
the  most  difficult  part  of  the  industry,  and  this  requires  hard  labor 
during  the  summer.  Stock-raising  of  one  kind  or  another  is  a  leading 
occupation  in  the  mountains  of  Norway,  Germany,  central  Asia, 
western  South  America,  western  United  States,  and  elsewhere. 

In  western  United  States  great  numbers  of  cattle  and  sheep  feed  on  the  grass 
of  the  public  domain  (land  owned  by  the  government) .  The  use  of  much  of  the 
public  domain  is  free  and  imrestricted.    While  this  has  had  its  advantages,  it 


MINING  IN  MOUNTAINS 


31S 


has  resulted,  at  many  times  and  places,  in  the  overstocking  of  the  range  (pasture 
land),  and  a  decrease  in  its  capacity.  Some  system  of  regulation  is  likely  to  be 
adopted  soon.     Grazing  in  the  National  Forests  is  regulated  now. 

Mining  in  mountains.  Many  mountains  contain  valuable  ore 
deposits,  and  mining  is  one  of  the  most  distinctive  of  mountain  indus- 
tries. The  original  source  of  most  of  the  valuable  metals  appears  to 
have  been  the  igneous  rocks  (hardened  lavas),  and  great  intrusions 
of  the  latter  form  the  central  cores  of  many  mountains.  The  metals 
probably  were  scattered  widely  through  the  igneous  rocks  to  begin 
with,  and  were  slowly  concentrated  into  ores  in  veins,  largely  by 


Fig.  222.     Bisbee,  Arizona,  a  city  which  grew  up  about  copper  mines. 

ground-waters  (p.  212).  These  veins  are,  for  the  most  part,  in  or 
near  the  igneous  rocks.  Many  of  them  have  been  exposed,  and  so  made 
available  to  man,  by  erosion.  The  iron  and  copper  of  the  Lake  Supe- 
rior region  occur  in  the  rocks  of  old,  worn-down  mountains.  Much 
of  the  gold  mined  in  the  West  has  come  from  igneous  rock,  and  from 
the  immediate  surroundings  of  great  intrusions  of  lava.  In  north- 
eastern Pennsylvania  the  folding  of  beds  of  rock  containing  layers  of 
coal  helped  to  change  the  latter  into  "  hard  coal "  or  anthracite.  Much 
of  the  coal  of  this  region  was  carried  away  later  by  erosion,  but  much 
was  preserved  in  the  down-folds  of  the  mountains  (Fig.  209).  More 
than  80,000,000  tons  of  this  coal  are  mined  yearly  (90,000,000  in  191 1), 
and  much  of  it  is  sent  throughout  eastern  and  central  United  States. 
Cities  have  grown  quickly  from  rude  mining  camps  following  the 
discovery  of  rich  mineral  deposits  (Fig.  222).  Thus  in  the  late 
1870 's  Leadville,  Colorado,  became  a  city  of  15,000  people  in  a 


3x6 


MOUNTAINS,  PLATEAUS,  AND  LIFE 


few  months,  though  in  a  sage-brush  valley  then  difficult  to  reach, 
and  at  an  elevation  of  10,000  feet.  Again,  important  mineral  de- 
posits may  help  to  gather  a  dense  urban  and  industrial  population 
about  the  borders  of  the  mountains  in  which  they  occur,  as  in  the  case 
of  the  Pennine  Mountains  of  north-central  England,  and  the  Erz 
(meaning  ore)  and  Riesen  ranges  of  Germany,  where  mining  has  been 
carried  on  for  many  years. 

Mountains  as  forest  reserves.  The  slopes  of  many  moun- 
tains have  been  left  largely  in  timber  because  unsuited  to  agricul- 
ture, and  various  mountain  ranges  now  support  important  lumber 


Fig.  223.  Modem  lumber  mill  in  the  Sierra  Nevada  Mountains,  California. 
(U.  S.  Forest  Service.) 

industries  (Fig.  223).  The  relation  of  mountain  forests  to  the  flow  of 
streams  rising  in  them,  and  to  the  problems  of  navigation,  water  power, 
irrigation,  and  soil  erosion  has  been  noted  (pp.  169,  290,  298).  These 
problems,  together  with  the  need  of  insuring  a  permanent  lumber  sup- 
ply, have  led  various  countries  to  regulate  the  use  and  cutting  of  moun- 
tain forests,  and  to  provide  that  certain  areas  remain  forest-covered^ 

Japan  has  many  steep  volcanic  mountains,  whose  slopes,  if  uncovered,  would 
be  eroded  rapidly  by  the  heavy  rains;  this  helps  to  explain  the  fact  that  nearly 
3/5  of  the  country  has  been  left  in  forest  reserves,  although  the  nation  is  in  great 
need  of  more  farm  land.     Among  European  countries,  Germany,  Switzerland,  and 


IMPORTANCE  OF  MOUNTAIN  FORESTS  317 

France  have  skillfully  managed  forest  reserves  on  mountain  slopes.  Some  of  the 
Mediterranean  countries  show  the  evils  wliich  may  follow  the  cutting  away  01 
mountain  forests.  In  Dalmatia,  for  example,  mountain  slopes  once  forested 
consist  now  of  bare  rock,  and  are  of  little  use  to  man.  In  parts  of  eastern  and 
northeastern  China  the  forests  are  gone,  and  one  may  travel  hundreds  of  miles 
without  seeing  a  single  grove  on  the  hill  sides.  Even  the  undergrowth  has  been 
destroyed,  and  in  places  all  grass  and  other  vegetation  suited  to  the  purpose  are 
gathered  for  the  cattle,  or  eaten  by  goats  and  sheep. 

Serious  results  have  followed:  (i)  Heavy  rains  cause  violent  floods.  Valleys 
usually  without  streams  may  be  occupied  suddenly  by  torrents  which  destroy 
bridges  and  buildings,  ruin  fields,  and  then  disappear  within  a  few  hours.  (2)  In 
many  places  not  enough  water  enters  the  ground  to  keep  the  water  table  sufficiently 
near  the  surface  for  the  good  of  plants.  (3)  Erosion  has  been  increased  enormously 
(Fig.  80).  Large  lowland  areas  are  covered  with  coarse  waste,  and  much  fine 
material  is  swept  into  the  sea.  (4)  Timber  is  at  a  premium.  In  the  western 
mountains  forest  destruction  is  less  advanced,  and  travelers  report  meeting 
long  lines  of  coolies  carrying  boards  down  to  the  plains,  where  they  are  worth  the 
equivalent  of  $2  to  $3  each,  a  value  which  restricts  their  use  to  special  purposes, 
such  as  making  coffins. 

Most  of  the  National  Forests  of  the  United  Stat,es  (p.  298)  are  in  the  moun- 
tainous districts  of  the  West  (Fig.  207),  where  the  greater  part  of  the  timber  is 
found  on  the  mountain  slopes  because  the  latter  receive  more  rain  than  the  sur- 
rounding plateaus  and  plains.  Congress  provided  in  191 1  for  a  National  Forest 
in  the  southern  Appalachians,  where  the  maintenance  of  a  forest  cover  on  many  of 
the  slopes  is  of  great  importance  (pp.  173,  221). 

Mountains  as  pleasure  resorts.  The  cool,  invigorating  sum- 
mer climate  and  beautiful  scenery  of  many  mountains  lead  thousands 
of  lowland  dwellers  to  visit  them  yearly.  The  mountains  of  New 
England,  the  Adirondacks,  Catskills,  and  parts  of  the  Alleghanies, 
contain  many  popular  resorts.  With  the  growth  of  population  in 
western  United  States,  the  mountains  of  that  section  probably  will 
be  visited  more  and  more. 

Most  of  the  National  Parks  (Fig.  224)  and  National  Monuments  are  in  the 
West,  and  a  number  of  them  contain  mountains  or  portions  of  mountains  of  unusual 
beauty  and  interest.  The  National  Parks,  of  which  there  are  13  in  continental 
United  States,  were  created  by  Congress,  and  serve  various  purposes;  they  are 
intended  especially  to  be  "play-grounds  for  the  American  people."  In  1905  the 
President  was  given  power  to  set  aside  from  the  public  domain  as  National  Monu- 
ments any  "historic  landmarks,  historic  or  prehistoric  structures,  or  other  objects 
of  historic  or  scientific  interest."  There  are  now  twenty-eight  National  Monu- 
ments, of  which  the  Mount  Olympus,  Washington,  and  Grand  Canyon,  Arizona, 
monuments  are  largest. 

The  Alps,  situated  in  the  midst  of  densely  settled  countries, 
are  the  most  beautiful  mountains  in  Europe,  and  have  come  to 
be  perhaps  the  greatest  summer  resort  in  the  world.     Hundreds 


3i8 


MOUNTAINS,  PLATEAUS,  AND   LIFE 


of  hotels  (Fig.  225)  depend  upon  the  tourist  trade,  and  the  enier- 
tainment  of  visitors  has  become  almost  a  national  industry. 

Other  mountain  resources  and  industries.  Fur-bearing  animals 
constitute  an  important  resource  of  some  mountain  regions.  They 
were  once  a  resource  in  many  others  where  few  are  left. 

From  about  1807  to  the  middle  of  the  century,  the  fur  trade  in  the  Rocky 
Mountains  of  the  United  States  was  of  great  value.  Trading  posts  were  estab- 
lished in  the  mountains  and  along  the  larger  rivers  flowing  eastward  from  them, 


Fig.  224.     Map  showing  distribution  of  National  Parks.  • 

at  which  a  driving  business  was  done.  St.  Louis  was  the  great  depot  and  outfitting 
point  of  the  trade.  The  trappers  and  traders  were  the  pathfinders  of  the  West. 
The  fur  trade  is  still  of  some  importance  in  the  mountains  of  western  Canada. 

We  have  seen  that  many  mountain  people  are  forced  to  make 
most  of  their  own  clothing,  implements,  utensils,  etc.  (p.  309).  In 
addition,  many  of  them  make  special  articles  of  superior  quality  for 
sale.  In  this  way  they  eke  out  a  living,  and  find  work  during  the 
winter  months  when  little  can  be  done  out  of  doors.  From  wood, 
metals,  wool,  or  other  raw  material  at  hand,  they  make  artistic  wares 
which  are  suited  to  mountain  transportation,  and  command  ready 
sale.  Such  are  the  carved  wooden  wares  of  the  Swiss,  and  the  lace 
made  by  some  of  the  Italian  mountaineers. 


ORIGIN  AND  EROSION  OF  PLATEAUS  319 

Many  mountain  streams  afford  much  water  power  (pp.  248,  256, 
290)  which  will  be  used  increasingly  in  the  future.  In  most  cases, 
however,  much  of  the  energy  will  be  carried  outside  the  mountains  in 
the  form  of  electricity,  to  be  used  in  the  lowlands. 

Plateaus 

Distribution.  As  stated  elsewhere  (p.  21),  large  plateaus  occur 
for  the  most  part  in  three  classes  of  situations,  (i)  Some  of  them  are 
between  a  lower  plain  on  one  side  and  higher  mountains  on  the  other, 


A  summer  hotel  in  the  High  Alps. 


(2)  some  are  between  mountain  ranges,  and  (3)  some  rise  abruptly 
from  the  sea,  or  from  narrow  coastal  plains. 

Origin.  Plateaus  are  formed  in  various  ways,  (i)  Some  have 
been  built  by  many  lava  flows,  like  the  Columbian  Plateau  of  the 
Northwest  (Fig.  104)  and  the  Deccan  Plateau  of  India  (2)  Adjacent 
land  may  have  been  worn  low  or  warped  down,  leaving  a  plateau.  (3) 
The  plateau  may  have  been  warped  or  faulted  above  its  surroundings. 

The  erosion  of  plateaus.  Like  mountains,  all  plateaus  will  be 
worn  down  to  lowlands,  if  not  made  high  again.  Mature  plateaus 
are  table-lands  well  dissected  by  streams;  the  surface  is  carved  into 
hills  (or  mountains)  and  valleys  (or  canyons),  and  slope  and  relief 
are  at  a  maximum.  Some  dissected  plateaus  are  called  mountains 
(e.  g.  the  Catskills,  p.  306).  In  one  sense  there  are  no  old  plateaus, 
for,  when  worn  low,  they  are  plains. 


320 


MOUNTAINS,  PLATEAUS,  AND  LIFE 


Conditions  of  life  on  plateaus.  The  conditions  of  life  on  high, 
dissected  plateaus  are  much  like  those  in  mountains  situated  similar- 
ly (PP-  309~3i8),  while  the  conditions  on  many  low  plateaus  resemble 
closely  those  on  neighboring  plains  (Chapter  XVIII) .  Large  plateaus 
in  continental  interiors  surrounded  by  mountains  are,  in  general, 
deserts,  and  subject  to  great  ranges  in  temperature.  Accordingly, 
they  are  settled  sparsely.  Farming  is  confined  for  the  most  part  to 
the  slopes  of  waste  at  the  bases  of  rain-catching  mountains,  where 
water  may  be  led  from  the  withering  streams  for  use  in  irrigation. 
The  greater  part  of  such  plateaus  is  uninhabited,  save  by  bands  of 
wandering  nomads,  as  in  central  Asia,  or  by  occasional  ranchmen 
whose  cattle  and  sheep  graze  on  the  thin  and  scattered  growth  of 
grass,  as  in  parts  of  western  United  States. 

The  habitability  of  a  high  plateau  is  influenced  greatly  by  its 
latitude;  while  such  a  plateau  is  cold  and  uninviting  in  the  temperate 
zone,  it  has  a  temperate  climate  in  the  tropics,  where,  if  other 
conditions  are  favorable,  it  may  have  a  population  much  denser  than 
that  of  the  neighboring  lowlands.  , 

Nearly  three-fourths  of  the  people  of  Bolivia  live  at  altitudes  of  6,000  to 
14,000  feet,  and  of  the  nine  most  thickly  settled  provinces,  five  are  at  elevations 
greater  than  11,000  feet.  Three-fourths  of  the  population  of  Ecuador  are  found 
in  the  plateau  basins  of  the  Andean  highlands,  at  an  average  elevation  of  8,000 
feet.  There  is  a  striking  contrast  also  between  parts  of  the  cool  plateau  and  the  hot 
lowlands  of  Mexico.  The  former  have  relatively  dense  and  progressive  popula- 
tions, v/nile  the  latter  are  settled  sparsely  by  backward  Indians.  In  higher  lati- 
tudes, plateaus  for  various  reasons  are  in  general  settled  much  less  densely  than  the 
neighboring  plain=,  as  already  indicated.  The  Great  Basin  and  Columbian 
Plateau  of  western  United  States  each  contained,  in   1900,  only  0.5  per  cent 

of  the  population  of  the  country.     In 


these  regions  the  population  num- 
bered only  1.6  and  3.2  persons,  respec- 
tively, per  square  mile.  The  sparsest 
population  of  Great  Britain  is  found 
in  the  Highlands  of  Scotland. 

Questions 

I.    (1)  In  what  stage  of  erosion 

are  the  mountains  shown  in  Fig.  226? 

(2)   How   will    the  slopes    of    these 

mountains  be  changed  in  the  future? 

2.    (i)  What  is  the  age,  in  terms  of  erosion,  of  the  mountains  shown  in  Fig.  208? 

(2)  What  was  the  topographic  age  of  the  surface  from  which  the  mountains  were 

formed?    The  evidence? 


Fig.  226.     Sketch  of  mountainous  region. 


QUESTIONS 


321 


3.  (i)  Compare  and  contrast  the  climate  of  the  mountains  and  plain  shown 
in  Fig.  227.  Why  the  differences?  (2)  What  work  are  the  streams  doing  in  the 
mountains?  On  the  plain?  Reasons  in  each  case?  (3)  What  kinds  of  soil  would 
you  expect  to  find  on  the  plain  just  west  of  the  mountains?    Why?     (4)  What 


1 

/-5 

^r^ 

j 

I -IS 

■ 

\     yi((& 

l^^^^g 

\  ^^"1     V  nS^ 

^S 

/ 

1   j,*^  ""^  1    (  // 

^^ 

^-^OT 

^^^m 

Fig.  227.    Portion  of  Paradise,  Nevada,  topographic  sheet.    Scale  4  miles 
per  inch.     (U.  S.  Geol.  Surv.) 


does  the  map  suggest  concerning  the  chances  for  successful  agriculture  in  the 
different  parts  of  the  area? 

4.  Compare  and  contrast  the  relations  of  mountains  to  the  life  of  (i)  primitive 
and  (2)  advanced  peoples. 

5.  Account  for  the  fact  that  houses  in  arid  plateaus  often  are  built  with  flat 
roofs  and  thick  walls. 


CHAPTER  XVIII 
PLAINS  AND   THEIR    RELATIONS   TO   LIFE 

Origin  and  classes  of  plains.  Various  types  of  plains  have  been 
discussed  in  previous  pages,  and  some  of  their  relations  to  human 
affairs  noted.  Rivers  make  flood-plains  (p.  236),  delta  plains  (p.  241), 
and  peneplains  (p.  227).  The  ancient  ice-sheets  formed  vast  drift 
plains  or  glacial  plaints  (p.  260).  The  floors  of  extinct  lakes  form  many 
nearly  flat  lake  plains,  especially  in  glaciated  regions  (p.  262),  Most 
lake  plains  are  small. 

Extensive  plains,  like  the  Atlantic  and  Gulf  coastal  plains  of 
the  United  States  and  the  vast  interior  plain  whiqji  stretches  from 
the  Appalachians  to  the  Rockies,  cannot  in  most  cases  be  put  in 
any  of  the  above  classes.  They  commonly  contain  many  smaller 
plains  of  several  or  all  of  the  t3TDes  mentioned.  In  general,  large 
coastal  plains  were  once  marginal  sea-bottoms,  and  were  made  into 
land  by  being  raised  or  by  the  sinking  of  the  sea.  Coastal  plains  may 
also  be  peneplains,  or  they  may  be  land  made  by  the  filling  of  a  shallow 
sec:  border  by  sediment  washed  from  the  land.  Large  interior  plains 
are  either  areas  worn  low,  or,  in  more  cases,  they  are  former  coastal 
plains  now  separated  from  the  sea  by  newer  land.  The  changes  made 
in  plains  by  erosion  were  discussed  in  Chapter  XV. 

Distribution  of  extensive  plains.  Most  of  the  great  plains  of 
the  world  are  in  the  northern  hemisphere.  The  northern  parts  of  the 
large  plains  which  border  the  Arctic  Ocean  are  of  little  value  to  man, 
but  there  are  vast,  fertile  plains  in  the  north  temperate  zone  which 
are  of  great  importance  in  the  life  of  the  world.  The  southern  conti- 
nents are  unfortunate  in  having  their  largest  lowlands  within  the 
tropics,  where  climatic  conditions  retard  human  progress. 

General  advantages  of  plains.  From  the  standpoint  of  human 
occupation,  plains  which  possess  a  favorable  climate  have  distinct 
advantages  over  mountains  and  plateaus.  In  general,  the  slopes 
of  plains  are  gentler,  their  soils  thicker  and  more  fertile,  and  they 
have  a  much  smaller  percentage  of  useless  land.    Their  advantages 

322 


PLAINS  AND  HUMAN  PROGRESS  323 

of  climate,  soil,  and  topography  make  plains  the  great  agricultural 
regions  of  the  world.  In  this  connection  it  should  be  remembered 
that  agriculture  is  the  basis  of  all  lasting  advance  in  civilization. 
Movement  is  relatively  easy  on  plains,  and  difficult  in  mountains 
(p.  307).  This  means  that  goods  and  ideas  circulate  more  readily, 
and  that  trade  and  culture  develop  more  rapidly,  among  lowland 
people.  In  mountains,  a  great  variety  of  conditions  may  be  found 
within  a  small  area,  while  on  plains,  similar  conditions  may  prevail 
over  large  areas.  It  follows  that  most  occupations  of  plains  have  a 
much  wider  distribution  than  those  of  mountains. 

Because  of  the  advantages  of  lowlands  for  agriculture  and  trade, 
the  great  majority  of  the  people  of  the  world  live  on  them.  The  rela- 
tively dense  populations  of  the  favored  lowlands  of  the  United  States 
are  shown  by  Fig.  281.  More  than  9/io  of  the  people  of  the  country 
live  on  lands  less  than  1,500  feet  above  the  sea.  While  this  shows 
that  most  of  the  people  live  on  plains,  it  will  be  remembered  that  there 
are  plateaus  and  mountains  lower  than  1,500  feet,  while  a  part  of  the 
Great  Plains  is  much  higher.  Less  than  i  per  cent  of  the  people  live 
at  elevations  of  more  than  6,000  feet. 

Contrasts  among  plains.  Apart  from  their  mode  of  origin,  plains 
differ  in  many  ways.  They  may  be  large  or  small,  high  or  low,  rough 
or  smooth,  forested  or  treeless,  fertile  or  infertile,  wet  or  dry,  and 
they  may  be  in  hot,  temperate,  or  cold  regions.  Furthermore,  there 
are  all  gradations  between  these  extremes.  These  differences  affect 
human  interests  in  important  ways,  many  of  which  have  been  noted. 

Relatively  small  plains  protected  by  natural  barriers,  rather  than  large,  open 
ones,  favor  early  progress  in  civilization.  A  small  area  hastens  advance  to  the 
agricultural  stage  (Why?),  and  as  the  population  increases,  laws  and  customs  are 
made  in  the  attempt  to  overcome  the  friction  which  goes  with  crowding.  The 
isolated  and  protected  plains  of  Greece  possessed  many  advantages  for  early 
progress.  On  the  other  hand,  all  parts  of  a  vast  plain  not  protected  by  barriers, 
such  as  that  of  Russia,  are  open  to  attack.  It  is  easy  for  the  people  of  a  large 
plain  to  scatter  in  search  of  game  and  other  food,  and  the  natural  food  supply  may 
be  sufficient  to  postpone  indefinitely  the  development  of  agriculture.  Extensive 
plains,  such  as  those  of  central  United  States,  afford  excellent  conditions  for  the 
further  progress  of  a  people  already  advanced  in  civilization.  This  is  especially 
true  where,  as  in  the  case  cited,  such  plains  have  varied  geographic  conditions 
and  resources  iri  their  different  parts. 

Climate  is  the  most  important  factor  affecting  the  life  of  exten- 
sive plains,  and  the  larger  plams  of  the  world  are  so  distributed 
with  reference  to  climate  that  the  conditions  of  life  in  them  may 


324  LIFE  IN  PLAINS 

be  discussed  briefly  under  the  following  headings:  (i)  Life  in  well- 
watered  plains  of  middle  latitudes.  (2)  Life  in  semi-arid  plains. 
(3)  Life  in  desert  plains.  (4)  Life  in  Arctic  plains.  (5)  Life  in 
humid  plains  of  low  latitudes.  The  more  important  direct  effects 
of  various  types  of  climate  on  life  were  discussed  in  Chapters  IX, 
X,  and  XI. 


Life  in  Well- Watered  Plains  of  Middle  Latitudes 

Plains  in  middle  latitudes  having  plenty  of  rain  are  the  seats  of 
advanced  civilizations,  and  some  of  them  support  dense  populations; 
The  soil  is  the  most  important  resource  of  these  plains,  and  agricul- 
ture the  most  wide-spread  occupation.  On  the  whole,  they  have 
less  in  the  way  of  forests,  minerals,  and  water  power,  than  many  high- 
lands have,  but  plains  are  by  no  means  without  these  resources.  Lum- 
bering and  mining  are  carried  on  at  many  points,  and  commerce  and 
manufacturing  are  developed  highly  in  the  thickly' settled  sections. 
In  the  complex  life  of  these  regions,  the  influence  of  geographic  con- 
ditions is  less  apparent  and  less  direct,  but  not  less  important,  than  in 
the  simpler  life  of  the  grasslands  and  deserts. 

Differences  in  soil,  in  the  form  of  the  land,  in  drainage,  etc.,  have  their  eflfect 
on  the  distribution  and  occupations  of  the  people.  The  influence  of  variations  in 
soil  is  especially  great,  and  may  be  seen  in  many  places.  In  the  glaciated  plains 
of  northern  United  States,  various  kinds  of  soil  may  occur  within  the  limits  of  a 
good-sized  farm.  Here  the  intelligent  farmer  is  likely  to  devote  each  type  of  soil 
to  the  particular  use  or  uses  to  which  it  is  adapted.  In  other  places,  the  character 
of  the  drift  over  several  or  many  square  miles  is  determined  by  the  nature  of  the 
underlying  rock,  so  that,  for  example,  an  area  of  sandy  drift,  over  sandstone,  may 
lie  beside  an  area  of  limey-clay  drift,  over  limestone.  In  a  certain  region  in  south 
central  Wisconsin,  the  condition  of  the  people  in  two  such  areas  is  very  different. 
The  area  of  fertile,  limey-clay  soil  is  said  to  have  been  settled  by  people  of  greater 
means,  while  the  sandy  area  was  occupied  by  poorer  people  not  in  a  position  to 
choose.  The  original  difference  appears  to  have  increased.  In  the  one  case,  there 
are  attractive  homes  with  modern  conveniences,  large  barns,  many  windmills, 
improved  roads,  and  many  well-equipped  schools;  in  the  other,  many  of  the  build- 
ings are  old  and  unpainted,  few  farms  have  windmills,  roads  are  poor,  and  some  of 
the  schools  are  in  an  unsatisfactory  condition. 

The  influence  of  soil  on  the  distribution  and  activities  of  people  may  be  seen 
on  a  larger  scale  in  various  parts  of  the  Atlantic  and  Gulf  coastal  plains.  In 
Alabama,  the  northern  part  of  the  state  is  underlain  by  old  rocks  (Fig.  228).  This 
part  was  land  when  the  area  of  the  coastal  plain  was  under  water.  Sediment 
washed  from  the  old  land  helped  to  make  the  strata  of  the  coastal  plain.  East 
and  west  across  the  middle  of  the  state  there  is  a  low,  nearly  level  belt  of  rich  soil, 
weathered  from  the  limestone  beneath.    This  is  the  inner  part  of  the  coastal  plaiR. 


HUMAN  RESPONSES  TO  SOIL  CONDITIONS       325 

From  its  southern  edge  the  ground  rises  rather  abruptly  some  200  feet,  because 
of  the  outcrop  of  more  resistant  beds,  and  then  slopes  gently  southward  to  the 
coast.  The  soils  of  this  outer  belt  are  much  poorer  than  those  of  the  inner  lowland, 
except  along  the  bottoms  of  the  larger  valleys,  where  there  are  deep,  fertile  loams. 
The  history  and  present  life  of  the  state  cannot  be  understood  apart  from  these  soil 
belts.     The  first  American  settlers,  typical  log-cabin  pioneers,  settled  for  the  most 


Lesslhanio^ 

^^10t025% 

^■a&tosofo 
^H  50%  and  over 


Fig.  228.  Fig.  229. 

Fig.  228.    Map  showing  principal  physiographic  provinces  of  Alabama. 

Fig.  229.     Map  showing  distribution  of  slaves  by  counties  in  Alabama  (i860). 
Figures  in  legend  indicate  percentages  of  the  total  population. 


part  in  the  rich  inner  lowland  and  along  the  fertile  valley  bottoms.  Later,  this 
was  seen  to  be  the  section  best  suited  to  the  growth  of  cotton,  and  many  of  the 
earlier  settlers  were  pushed  by  the  slave-owning  planters  north  into  the  foothills 
of  the  mountains,  or  south  into  the  sandy  areas  of  the  outer  coastal  plain.  The 
inner  lowland  contained  the  largest  number  of  slaves  at  the  time  of  the  Civil  War 
(Fig.  229),  and  more  than  3/^  of  its  present  population  are  negroes.  The  outer 
zone  of  the  coastal  plain  always  has  had  a  relatively  sparse  population,  except  along 
the  larger  valleys.  There  are  still  extensive  pine  forests  where  lumbering,  the 
making  of  turpentine,  and  grazing  are  leading  industries.  Mobile  is  the  only 
important  city  in  this  part  of  the  state.  It  has  a  harbor  at  the  drowned  mouths  of 
the  leading  rivers  of  the  region,  and  is  the  natural  gateway  into  the  state  from  the 
south. 


326 


LIFE  IN  PLAINS 


Life  in  Semi-Arid  Plains 

Large  semi-arid  plains  occur  in  the  belt  of  the  trade-winds,  where 
some  of  them  merge  into  deserts,  as  in  northern  Africa  and  Australia. 
Others  lie  in  the  interiors  of  continents,  where  the  prevailing  winds 
which  reach  them  have  been  robbed  of  most  of  their  moisture  in  pass- 
ing over  mountains.  The  steppes  of  western  Asia  and  the  Great 
Plains  of  the  United  States  are  examples.  The  scanty  rainfall  of  such 
plains  or  its  unfavorable  distribution  prevents  the  growth  of  most 


Fig.  230. 
Adams.) 


Home  of  native  nomad  of  Argentine  Patagonia.      (Harriet  Chalmers 


trees  except  along  the  streams,  and  restricts  useful  vegetation  to  quick- 
growing  grasses  and  a  few  other  hardy  types  of  plants. 

Hunting  tribes  and  pastoral  nomads.  Under  primitive  con- 
ditions, the  inhabitants  of  semi-arid  plains  get  their  support  from 
flocks  and  herds,  or  depend  on  the  chase,  like  the  buffalo-hunting 
tribes  of  earlier  years  on  the  Great  Plains  (p.  328).  Both  the  pursuit 
of  game,  and  the  frequent  need  for  fresh  pastures  with  new  supplies 
of  water,  cause  the  people  to  lead  a  nomadic  life.  The  dwellings  must 
be  such  that  they  can  be  moved  easily  (Fig.  230);  in  many  cases 
they  are  tents  of  skins,  or  of  felt  made  from  wool.  Personal  effects 
and  household  utensils  are  few  and  light;  and  the  most  desirable  form 
of  wealth  is  flocks  or  herds,  which  transport  themselves. 


LIFE  IN  SEMI-ARID  UNITED   STATES  327 

The  movements  of  many  pastoral  tribes  are  regulated  by  the 
seasons.  In  some  cases,  their  flocks  and  herds  are  driven  in  summer 
into  the  highlands,  thus  escaping  from  the  hotter  plains  and  using 
more  of  the  pasturage.  The  Kirghiz  of  Russian  Turkestan  regularly 
take  their  flocks  in  summer  up  into  the  Altai  Mountains,  and  bring 
them  back  to  the  lower  lands  in  winter.  Again,  the  more  abundant 
grass  and  water  of  the  rainy  season  may  permit  the  people  to  gather 
in  considerable  groups  in  desirable  localities,  while  in  the  dry  season 
they  are  forced  to  scatter  widely,  to  secure  food  for  their  animals. 

The  pastoral  nomads  of  semi-arid  plains  always  have  been  maraud- 
ers and  conquerors,  though  less  so  than  the  men  of  the  desert  (p. 
S^T,).  Under  favorable  conditions,  their  growing  herds  and  flocks 
require  more  and  more  pasture,  and  from  time  to  time  compel  them 
to  move  beyond  the  boundaries  within  which  they  formerly  had 
roamed.  On  the  other  hand  a  long  and  severe  drought,  resulting  in  less 
pasturage  and  a  failing  water  supply,  or  disease  among  their  animals, 
may  bring  them  to  the  verge  of  famine,  and  drive  them  to  pillage  and 
conquest.  Mounted  on  horses  or  camels,  the  nomads  are  able  to 
make  swift  attacks  on  the  people  of  neighboring  lands,  and  to  retreat 
quickly  with  their  booty.  For  centuries,  portions  of  agricultural 
Russia  were  pillaged  repeatedly  by  hordes  of  horsemen  from  the 
southeastern  steppes,  and  the  Great  Wall  of  China  was  built  as  a  pro- 
tection against  pastoral  nomads. 

In  general,  it  may  be  said  that  the  conditions  of  life  in  semi- 
arid,  grassy  plains  rarely,  if  ever,  permit  their  native  tribes  to  develop 
more  than  a  low  form  of  civilization. 

Use  of  semi-arid  plains  by  civilized  people.  Even  where 
civilization  is  advanced,  plains  that  are  too  dry  for  agriculture  by 
ordinary  methods  are  devoted  largely  to  the  grazing  industry.  Vast 
semi-arid  areas  are  used  in  this  way  in  the  United  States,  Argen- 
tina, Australia,  and  Russia.  By  means  of  irrigation  and  special 
methods  of  cultivation,  agriculture  doubtless  will  be  extended  great- 
ly in  semi-arid  regions  in  years  to  come. 

The  Great  Plains.  The  history  of  the  western  portion  of  the 
Great  Plains  illustrates  many  of  the  conditions  of  life  in  semi-arid 
regions.  Until  after  the  Civil  War,  these  plains  were  occupied  by 
Indians  dependent  for  a  living  on  the  great  herds  of  buffaloes.  The 
kiUing  of  the  buffalo  and  the  confining  of  the  Indians  to  certain  areas 
(reservations)  opened  the  plains  to  the  cattle  industry.  In  the  drier 
parts  most  attempts  to  farm  by  ordinary  methods  have  been  un- 


328  LIFE  IN  PLAINS 

successful,  though  here  and  there  streams  and  wells  furnish  water  for 
irrigation  (p.  329).  Within  the  last  few  years,  "dry  farming" 
(p.  329)  has  replaced  the  grazing  industry  in  some  places. 

As  already  indicated,  the  buffalo  v/as  the  most  important  factor  in  the  lives  of 
many  Indians  of  the  Great  Plains.  The  chase  required  many  quick  moves,  and 
this  helped  to  keep  families  rather  small,  the  houses  light  and  portable,  and  personal 
property  small  in  amount.  Individual  ownership  of  land  was  unknown  among 
some  of  the  tribes.  The  mythology  of  the  Indians  was  tinged  by  their  hunting 
and  military  habits.  The  chiefs  attained  their  positions  because  of  their  skill  as 
hunters  or  warriors.  With  the  disappearance  of  the  buffaloes,  the  hunting  tribes 
lost  their  chief  support,  and  became  dependent  on  the  white  man.  Great  numbers 
of  buffaloes  were  killed  as  food  for  the  construction  gangs  of  western  railroads, 
and  for  their  hides,  which  were  in  great  demand  in  the  East  for  robes,  belting  for 
machinery,  and  other  purposes.  They  practically  disappeared  from  the  southern 
plains  in  the  middle  seventies,  and  from  the  northern  plains  a  few  years  later. 

The  stock-raising  industry  of  the  Great  Plains  began  in  Texas  and  spread  north- 
ward. Cattle  were  introduced  into  Mexico  by  the  Spaniards  about  1525,  and  before 
the  Revolutionary  War  there  were  large  cattle  ranches  nortlj  of  the  Rio  Grande. 
In  the  middle  1850's,  most  of  Texas  was  "a  vast,  unfenced  feeding  ground  for 
cattle,  horses,  and  sheep."  At  the  close  of  the  Civil  War,  cattle  were  very  cheap 
in  Texas,  but  brought  high  prices  and  were  in  great  demand  in  the  northern  cities. 
As  a  result,  the  practice  was  developed  of  driving  cattle  northward  in  great  herds 
to  shipping  points  on  the  railroads  that  were  then  building  across  the  Great  Plains 
in  Kansas  and  Nebraska.  The  "cow  towns,"  as  the  shipping  points  were  called, 
were  established  beyond  the  farming  frontier,  preferably  where  there  was  a  good 
supply  of  water  and  grass.  The  business  shifted  west  and  south  with  the  advancing 
railroads,  keeping  in  front  of  the  farming  zone.  The  banner  year  of  the  Texas 
cattle  drive  was  1884,  when  1,000,000  cattle  were  driven  out  of  the  state.  Soon 
after,  the  drives  were  rendered  unnecessary  by  the  extension  of  railroads,  which 
took  the  stock  to  market  in  much  less  time  and  usually  in  better  condition.  The 
stocking  of  the  northern  lands  occurred,  for  the  most  part,  after  1870,  and  before 
the  close  of  another  decade  the  business  had  spread  to  the  Canadian  boundary. 
For  a  time,  large  returns  were  realized  from  feeding  cattle  on  the  public  grass. 
Many  people  accordingly  went  into  the  business,  and  in  numerous  places  the  range 
(unfenced  pasture  land)  was  overstocked  and  the  pasturage  injured.  One  result 
of  this  in  many  places  was  the  introduction  of  sheep,  which  can  live  on  pasturage 
that  will  not  support  cattle.  The  conflicting  interests  of  cattlemen  and  sheepmen 
have  caused  much  trouble  in  some  of  the  grazing  states.  The  development  of  the 
grazing  industry  on  the  Great  Plains  had  an  important  influence  upon  the  growth 
of  the  slaughtering  and  meat-packing  industry  in  Kansas  City,  Omaha,  St.  Louis, 
Chicago,  and  (later)  South  Omaha,  from  which  meat  products  were  sent  to  the 
urban  and  industrial  centers  of  the  northeastern  states  and  Europe. 

In  1880,  the  Great  Plains  west  of  the  98th  or  99th  meridian  were  occupied  only 
by  stockmen,  except  along  some  of  the  larger  valleys  (Fig.  231).  A  few  years  later 
thousands  of  farmers  moved  there  and  began  to  grow  wheat,  using  the  seed  and 
methods  which  they  had  employed  farther  east,  where  the  rainfall  is  greater.  The 
population  of  Kansas  increased  250,000  between  1885  and  1888,  largely  in  the 


FUTURE  USE  OF  SEMI-ARID  LANDS 


329 


western  portion  (Fig.  23 2) .  The  agricultural  invasion  began  because  of  heavy  rains 
in  the  middle  eighties,  and  was  kept  up  for  a  few  years  by  the  advertising  of  railroads 
and  the  activity  of  town-builders  and  land-dealers.  Then  came  several  very  dry 
years,  and  thousands  were  starved  out  of  the  region.  Kansas  lost  some  200,000 
people,  and  the  western 
parts  of  Nebraska,  the  Da- 
kotas,  and  the  eastern  part 
of  Colorado  were  affected 
similarly  (Fig.  233).  Mil- 
lions of  acres  returned 
slowly  to  grass,  and  within 
a  few  years  hundreds  of 
"cities"  were  abandoned 
by  their  founders.  Within 
the  last  few  years,  another 
agricultural  invasion  of  the 
High  Plains  has  been  in 
progress.  A  series  of  wet 
seasons,  the  activity  of  land 
companies,  and  the  intro- 
duction of  agricultural  me- 
thods adapted  to  semi-arid 
conditions  have  been  the 
leading  causes.  The  out- 
come is  still  uncertain,  but 
is  not  likely  to  be  so  disas- 
trous as  the  first  settlement, 
because  men  know  better 
now  how  to  make  use  of 
dry  lands. 

The  chief  uses  to  which 
the  semi-arid  parts  of  the 
Great  Plains  will  probably 
be  put  in  the  future  may 
be  suggested  briefly,  (i) 
Farming  by  irrigation  will 
be  extended  somewhat,  but 
the  amount  of  water  avail- 
able from  all  sources  is  but 

a  small  fraction  of  what  would  be  needed  to  irrigate  all  the  land.  (2)  Dry-farming, 
especially  with  hardy,  drought- resisting  plants  (p.  173),  promises  much  more  than 
irrigation  for  the  region  as  a  whole.  Dry- farming  scarcely  can  be  said  to  have 
passed  the  experimental  stage,  and  how  large  an  area  can  be  dry-farmed  success- 
fully is  quite  uncertain.  As  already  pointed  out  (p.  65),  dry-farming  seeks  (a) 
to  get  the  largest  possible  amount  of  the  rainfall  to  enter  the  ground,  and  (b)  to 
reduce  to  a  minimum  the  loss  of  water  by  evaporation  from  the  soil.  (3)  Stock-rais^ 
ing,  and  stock-raising  with  subordinate  farming,  apparently  must  remain  the 
leading  industries  over  large  areas. 


232.  Fig.  233. 

Figs.  231,  232,  233.  Maps  showing  distribution 
of  population  on  the  western  Great  Plains  in  1880, 
1890,  and  1900. 


330  LIFE  IN  PLAINS 

Life  in  Arid  Plains 

About  Vs  of  the  land  is  desert  for  lack  of  rain.  By  no  means  all 
dry  deserts  are  plains;  some  are  plateaus,  and  within  desert  plains  and 
desert  plateaus  there  may  be  ranges  of  high  hills  and  mountains 
(p.  334),  though  these,  in  most  cases,  receive  more  rain  than  their  sur- 
roundings. Many  of  the  conditions  of  life  are  similar  in  arid  plains 
and  plateaus,  and  they  are  considered  together.  Life  in  cold  deserts, 
such  as  parts  of  the  Arctic  plains  (p.  336),  differs  greatly  from  that 
in  dry  deserts.    Only  the  latter  are  considered  here. 

The  great  deserts  of  the  world  are  in  the  zones  of  the  trade-winds, 
or  to  leeward  of  high  mountains.  Their  wide  distribution  and  vast 
extent,  the  location  of  some  of  them  near  well-watered  and  thickly- 
settled  regions,  and  the  relations  of  their  people  to  their  neighbors, 
always  have  given  deserts  great  importance  in  the  life  of  the  world. 
Except  in  the  relatively  small  areas  where  irrigation  is  possible,  or  to 
which  people  may  be  attracted  by  valuable  mineral  deposits,  deserts 
are  doomed  to  have  scanty  populations. 

The  power  of  mineral  deposits  to  bring  people  to  deserts  is  illustrated  strikingly 
in  Nevada.  The  deposits  of  gold  and  silver  first  discovered  there  attracted  thou- 
sands of  miners  and  prospectors,  and  made  Nevada  a  state  in  five  years.  Later, 
the  population  of  the  state  declined  greatly  (p.  311),  but  in  the  last  decade  it  has 
increased  again  (Si.ooo  in  1910)  due  to  new  discoveries  of  ore.  Butte,  Montana, 
a  city  of  39,000  inhabitants,  is  supported  largely  by  deposits  of  copper  that  underlie 
less  than  two  square  miles  of  arid  land  which,  without  the  mines,  could  support 
only  a  few  people. 

Plant  life  in  deserts.  Plants  require  water  for  growth,  and 
they  lose  water  chiefly  by  evaporation  from  their  leaves.  It  is  clear 
that  plants  with  unusual  ability  to  get  and  store  water,  and  plants 
which  lose  but  little  water,  are  best  suited  to  deserts.  Most  desert 
plants  are  provided  with  many  long  roots,  which  enable  them  to  get 
more  moisture  from  the  dry  soil  than  would  be  possible  otherwise, 
and  at  the  same  time  help  them  to  stand  against  the  winds,  often  of 
great  strength.  The  loss  of  water  from  the  plant  is  reduced  by  such 
things  as  thick  skins,  corky  bark,  and  coats  of  hair.  Some  desert 
plants  have  no  leaves,  and  some  have  only  a  few  small,  rounded,  and 
fleshy  leaves.  Thus  the  loss  of  water  by  evaporation  is  diminished. 
Many  desert  plants  have  thorns,  spines,  and  unpleasant  or  poisonous 
juices,  which  help  to  protect  them  against  devouring  animals.  Scat- 
tered shrubs  and  coarse  grasses  are  among  the  leading  types  of  desert 


THE  ANIMALS  OF  DESERTS  331 

vegetation.  Fig.  234  shows  desert  plants  of  various  kinds.  The 
plants  of  deserts  have  little  economic  value  at  the  present  time.  The 
vegetation  of  oases  (p.  334)  is  quite  unlike  that  of  the  desert. 

After  rain  falls  in  the  desert,  many  small,  quick-growing  plants  spring  up, 
some  of  which  bear  bright  flowers;  but  soon  they  wither  and  die  for  lack  of  sufficient 
water. 

Animal  life  in  deserts.  Like  certain  plants,  some  animals  have 
developed  characteristics  which  help  them  to  live  in  the  desert. 
The  severity  of  desert  conditions  is  shown,  however,  by  the  small 


'    .0^. 

iJIC^^' 

B^^^jt 

&, 

b 

^^ 

mmi 

Ml 

Fig.  234.    View  in  the  desert  near  Tucson,  Arizona.     (W.  L.  Tower.) 

number  and  the  small  variety  of  animals  which  can  endure  them. 
Like  desert  plants,  desert  animals  are,  as  a  rule,  scattered.  Some 
are  very  fleet  of  foot,  and  thus  are  able  to  move  between  widely 
separated  watering  places  and  to  escape  from  their  enemies.  Some; 
are  slow-moving,  but  most  of  these  are  venomous,  and  all  of  therm 
are  able  to  go  without  water  for  long  periods,  A  desert  is  an  im- 
passable barrier  to  slow-moving  animals  which  need  water  frequently. 
On  account  of  the  hot  days  and  cool  nights,  many  desert  animals 
are  more  active  during  the  night  than  during  the  day.  Many  of 
them  are  dull  of  color,  and  not  easily  seen  against  the  barren  ground. 

The  camel  is  the  most  important  animal  of  the  arid  regions  of  the  Old  World, 
having  long  been  called  "the  ship  of  the  desert."  It  is  found  in  northern  Africa 
and  in  Asia  (Fig.  235),  from  Arabia  to  China,  and  northward  to  northern  Mon- 
golia. A  draft  camel  carries  300  to  600  pounds,  according  to  size,  the  customary 
load  being  about  ^  the  weight  of  the  animal.  It  is  said  that  caravans  sometimes 
travel  20  out  of  the  24  hours  at  a  steady  gait  of  2>^  to  3  miles  an  hour,  halting 
only  during  the  hottest  part  of  the  day. 


332 


LIFE  IN   PLAINS 


The  camel  is  well  suited  to  desert  conditions.  It  can  travel  far  with  a  small 
supply  of  food  and  water;  it  has  small  nostrils,  which  can  be  closed  so  as  to  prevent 
the  entrance  of  the  finest  wind-driven  sand;  eyes  protected  against  sand  and  sun  by 
long,  heavy  lashes;  and  peculiar  padded  feet,  fitted  for  the  hot  sands.  The  parts 
of  the  body  exposed  most  to  heat  and  friction  are  protected  by  great  callosities. 
When  at  rest  in  an  oasis,  a  camel  drinks  only  enough  for  the  time  being,  but  when 
on  the  march  it  makes  provision  for  many  hours  in  advance.  During  weeks  of  rest 
or  light  work,  the  hump  increases  in  size;  on  long  journeys,  the  material  of  the 
hump  is  absorbed  into  the  system,  keeping  up  the  strength  of  the  animal. 

Human  responses  to  desert  conditions.  Agriculture  is  impos- 
sible in  deserts,  without  irrigation,  and  few  places  have  enough 
water  for  that.     Furthermore,  grazing  in  many  cases  is  possible  only 


Fig.  235.    Camels  in  northwestern  India, 
come  through  Khyber  Pass  from  Afganistan. 


A  portion  of  a  caravan  which  has 


along  the  margins  of  the  desert,  or  in  oases.  Since  deserts  afford 
little  food,  they  can  support  few  people,  scattered  widely  in  small 
groups.  The  conditions  in  deserts  permit  native  tribes  to  make  little 
progress  in  civilization. 

Along  the  borders  of  many  deserts  the  conditions  of  life  are  a 
continuation  of  those  in  semi-arid  grasslands  (p.  326).  The  people 
wander  from  place  to  place  with  their  flocks  and  herds,  the  size  of 
the  social  group  being  determined  by  the  supply  of  water  and  grass. 
Along  the  margins  of  certain  deserts,  the  people  sometimes  do  a 
little  farming  when  the  water  supply  permits,  to  add  to  the  often 
uncertain  and  always  restricted  living  afforded  by  their  animals. 

We  have  seen  (p.  331)  that  deserts  may  support  considerable  vegetation  for  a 
short  time  after  rain  falls.  Along  the  edges  of  certain  deserts,  pasturage  is  available 
ia  the  wet  season,  even  where  the  surface  is  bare  in  the  dry  season.    This  may 


THE   MEN  OF  THE  DESERT  335 

control  the  seasonal  migrations  of  pastoral  tribes.  In  winter,  the  Arabs  find  scant 
pasturage  for  their  goats  and  sheep  on  the  northern  border  of  the  Sahara;  in 
summer,  they  drive  them  to  the  slopes  of  the  Atlas  Mountains.  In  the  same  way 
flocks  and  herds  are  driven  at  various  points  into  the  southern  edge  of  the  Sahara 
in  summer,  which  is  there  the  rainy  season. 

The  arts  of  desert  people  are  primitive  and  confined  largely  to 
household  industries.  Making  leather  and  leather  utensils  from  the 
skins  of  animals,  pottery  from  clay,  and  blankets  and  rugs  from  wool 
furnished  by  the  flocks,  are  typical  industries. 

Among  American  Indians,  the  potter's  art  was  developed  best  in  the  arid 
Southwest.  Here  water  was  scarce,  and  durable,  water-tight  vessels  were  an 
absolute  necessity.  The  Navajo  Indians  of  this  region  possess  large  flocks  of 
sheep,  and  sell  wool  and  blankets.  The  latter  are  made  by  the  women  in  many 
artistic  designs,  and  enjoy  a  wide  reputation. 

From  force  of  necessity,  most  wandering  desert  tribes  are  rob- 
bers. They  pillage  caravans  and  hold  travelers  for  ransom,  or  exact 
heavy  tolls  in  return  for  safe  passage  through  the  desert.  They  raid 
adjacent  agricultural  lands,  and  in  some  cases  have  levied  regular 
tribute  upon  them,  or  have  conquered  and  settled  in  them.  The 
Sudan  and  Egypt  have  been  invaded  repeatedly  by  tribes  from  the 
Sahara. 

The  people  of  deserts  are  excluded  more  or  less  completely  from 
the  culture  of  the  outside  world.  Hence,  as  in  mountains  (p.  309), 
old  manners  and  customs  persist.  Customs  of  the  time  of  Christ 
still  are  observed  in  the  desert  of  Arabia.  Scattered  widely  in  small 
groups,  desert  people  develop  many  dialects.  They  are  compelled 
to  eat  very  sparingly  of  the  few  things  available.  Nothing  is  wasted; 
the  Tibbus  of  the  Sahara  eat  even  the  skins  and  powdered  bones  of 
their  dead  animals.  The  scanty  diet  and  severe  hardships  incident 
to  life  in  the  desert  help  to  produce  a  distinct  physical  type.  The  men 
are  commonly  thin,  but  wiry,  and  capable  of  great  exertion.  Desert 
nomads  have  great  powers  of  observation  and  a  remarkable  sense  of 
locality.  Intellectual  activity  necessarily  is  restricted  in  the  desert. 
The  dull  scenery  and  the  lonely  life  tend  to  lead  the  mind  into  reverie 
and  contemplation.  The  majesty  of  the  larger  deserts,  their  vast 
extent,  their  great  dust  and  sand  storms,  and  the  uncertain  position 
of  man,  all  tend  to  inspire  feelings  of  awe  and  reverence.  It  is  sig- 
nificant that  Christianity  and  Mohammedanism  were  associated  close- 
ly in  their  origin  and  development  with  the  arid  and  semi-arid  regions 
of  the  Old  World. 


334  LIFE  IN   PLAINS 

Life  in  oases.  In  deserts,  permanent  settlements  based  on 
agriculture  are  possible  only  in  oases,  where  there  is  water  supplied 
by  springs,  artesian  wells,  or  rivers.  The  source  of  the  water  supply 
may  be  outside  the  desert  in  well-watered  regions,  or  within  the 
desert  where  elevations  rise  high  enough  to  compel  the  passing 
winds  to  give  up  a  part  of  their  moisture. 

The  Nejd  Plateau,  in  the  heart  of  Arabia,  rises  to  an  elevation  of  more  than 
5,000  feet,  and  here  there  are  fertile  oases,  cultivated  for  centuries,  and  extensive 
pastures.  Even  in  the  Sahara,  there  are  a  few  mountains  which  receive  enough 
rain  to  support  trees.  The  streams  formed  on  these  mountain  slopes  disappear 
after  descending  to  the  desert.  Some  of  the  narrow  valleys  are  farmed,  and  grazing 
is  possible  over  larger  areas. 

Some  oases  serve  merely  as  headquarters  for  tribes  which  roam 
over  the  surrounding  desert  in  search  of  pasturage,  and  of  caravans 
which  they  may  attack.  Some  support  towns,  most  of  which  are 
small.  In  general,  the  larger  towns  are  located  on  the  main  caravan 
routes,  where  there  is  better  opportunity  for  trade  (p.  335).  The 
houses  in  many  cases  are  built  of  stone  or  adohe  (sun-dried  clay). 
In  many  cases,  oases  are  cultivated  most  carefully  in  order  to  secure 
the  largest  possible  returns  from  the  restricted  area  which  can  be 
watered. .  Vegetables,  cereals,  and  fruits,  especially  dates,  are  grown 
in  the  oases  of  the  Sahara  and  the  deserts  of  southwestern  Asia. 

The  date  palm  has  a  trunk  in  some  cases  fifty  to  sixty  feet  high,  ending  in  a 
great  crown  of  feathery  leaves  (Fig.  236).  Bearing  trees  average  from  100  to  200 
pounds  of  dates  a  year,  though  yields  of  500  or  600  pounds  have  been  known. 
A  tree  may  bear  fruit  for  a  century.  The  date  palm  is  adjusted  perfectly  to 
conditions  in  the  oases  of  low-latitude  deserts,  for  it  requires  a  dry,  hot  climate, 
and  a  moist  soil.  It  has  been  said  with  truth  that  the  Arabs  built  their  lives  on  the 
•date  palm.  In  the  future,  the  date  palm  probably  will  have  commercial  value  in 
irrigated  lands  along  the  lower  Colorado  River  (p.  242)  and  about  Phoenix,  Arizona. 

Oases  in  deserts  are  in  striking  contrast  with  the  barren  land 
about  them,  though  most  of  them  are  not  such  delightful  gardens  as 
they  have  been  described.  They  are  subject  to  frequent  sand-storms, 
their  water  supply  is  small  and  in  many  cases  impure,  and  their  prod- 
ucts are  restricted  in  variety  and  in  quantity. 

Commerce  of  the  desert.  Where  a  desert  lies  between  well- 
watered  and  populous  regions,  important  trade  may  be  carried  on 
across  it.  Some  trade  is  carried  on  also  between  agricultural  lands 
and  the  borders  of  neighboring  deserts,  because  of  their  contrasted 
resources  and  the  desire  of  the  desert  people  to  supplement  their 


TRADE  IN  THE  DESERT 


33S 


meager  products.     Timbuctoo,  on  the  Niger  River,  and  Damascus, 
in  Syria,  are  examples  of  places  which  serve  as  gateways  to  deserts. 

For  centuries,  goods  were  carried  in  large  quantities  across  the  vast  deserts  of 
central  and  western  Asia  only  by  pack  animals,  especially  the  camel,  and  even  to- 
day this  is  the  case  over  much  of  the  region  (Fig.  235).  A  number  of  caravan 
routes  cross  the  Sahara,  ex- 
tending from  oasis  to  oasis. 
The  trade  which  originates 
or  terminates  in  the  Sahara 
is  largely  in  dates,  salt, 
clothing,  cereals,  and  camels, 
while  for  centuries  the 
through  trade  has  included 
such  things  as  ivory,  gums, 
spices,  and  gold  dust. 
Prince  Henry  of  Portugal 
learned  of  the  trans-Saharan 
trade  while  on  an  expedition 
against  the  Moors  in  north- 
em  Africa  in  1415,  and 
partly  with  the  idea  of 
diverting  the  trade  of  the 
Guinea  Coast  to  his  own 
country  by  water,  he  began 
the  long  series  of  explora- 
tions along  the  coast  of 
Africa  which  culminated  in 
the  discovery  of  the  all- 
water  route  to  India.  The 
use  of  the  latter  route  to  the 
East  injured  greatly  the 
caravan  trade  across  Asia. 
A  trans-Saharan  railroad  is 
now  projected. 

Political  conditions 
in  deserts.  The  hard 
conditions  of  life  in 
deserts  repeatedly  have 
driven  their  inhabitants 


Fig.    236.     Date 
Biskra,  Algeria. 


palms    loaded    with    fruit. 


out  to  conquer  other  regions  (p.  333).  On  the  other  hand,  the  con- 
quest of  deserts  from  without  always  has  been  attended  by  great 
difficulties,  and  in  some  cases  never  has  been  accomplished.  The 
love  of  freedom  and  the  fighting  ability  characteristic  of  desert 
peoples,  in  addition  to  the  difficulties  which  an  invading  army  finds 
in  the  lack  of  roads,  water,  and  food,  have  helped  to  produce  this 


536 


LIFE  IN  PLAINS 


result.    Furthermore,  the  scant  resources  of   deserts  have  made 
them  relatively  uninviting  to  outside  people. 

Life  in  Arctic  Plains 

The  plains  which  border  the  Arctic  Ocean  are  known  as  barren 
lands  in  North  America,  and  as  tundras  in  Eurasia.  They  are  cold 
deserts,  snow-covered  for  some  two-thirds  of  the  year.  The  short  sum- 
mers, low  temperatures,  and  cold  or  frozen  soil  prevent  agriculture, 
and  restrict  vegetation  chiefly  to  stunted  bushes,  mosses,  and  various 
quick-growing,  flowering  plants.  The  few,  widely  scattered  inhabit- 
ants of  the  tundras  depend  largely  on  their  herds  of  reindeer  and  on 


Fig.  237.     Reindeer  and  sledge. 

hunting  for  their  hving.  Fishing  is  an  important  occupation  during 
the  three  or  four  months  when  the  streams  are  free  from  ice.  A 
nomadic  life  results  from  the  necessity  of  following  the  game  and 
the  reindeer  herds,  which  wander  half-free  in  search  of  pasturage. 
As  in  the  steppes  and  dry  deserts,  this  nomadic  life  means  small, 
easily  transported  dwellings  —  in  many  cases  a  tent  consisting  of  a 
framework  of  poles  covered  with  skins  —  and  few  and  simple  house- 
hold goods.  Some  of  the  tribes  move  northward  with  their  herds 
in  the  summer,  and  return  to  pass  the  winter  in  the  forests  which 
border  the  tundras  on  the  south.  Here  the  timber  affords  some 
shelter,  feed  is  available  for  the  reindeer,  and  game  may  be  hunted 
for  food  and  fur. 


THE   NATIVES  OF  TROPICAL  FORESTS  337 

All  that  the  camel  is  to  the  inhabitants  of  low-latitude  deserts,  the  reindeer  is 
to  the  men  of  the  Arctic  desert.  It  is  indifferent  to  cold,  and  is  an  excellent  draft 
animal  (Fig.  237).  Its  milk  and  flesh  are  used  for  food;  its  bones  and  horns  afford 
material  for  making  various  i  mplements ;  its  tendons  and  sinews  serve  for  thread ;  and 
its  skin  is  used  for  shelter  and  clothing.  The  reindeer  is  the  most  desirable  form 
of  wealth  on  the  tundra.  In  some  places,  a  herd  of  50  head,  which  will  support 
a  family  of  four  or  five,  requires  between  4  and  5  square  miles  of  tundra  pasturage. 
This  means  at  best  a  very  sparse  population. 

Some  years  ago  the  United  States  Government  imported  nearly  1,300  reindeer 
from  Siberia,  for  the  benefit  of  the  natives  of  northern  Alaska.  The  herds  have 
increased  rapidly,  and  are  proving  of  great  value. 

In  the  Arctic  plains  life  is  a  constant  struggle  for  food,  clothing, 
and  shelter.  There  is  little  opportunity  for  trade.  Situated  on  the 
outskirts  of  the  inhabited  world,  the  frozen  deserts  of  the  north  have 
played  a  much  less  important  part  in  history  than  the  centrally- 
located  deserts  of  lower  latitudes.  Nor  does  it  seem  likely  that  they 
can  become  of  much  importance  in  the  future. 

Life  in  Humid  Plains  of  Low  Latitudes 

Near  the  equator,  the  climate  of  the  lowlands  is  characterized 
by  heavy  and  frequent  rains,  and  by  high,  nearly  uniform  tempera- 
tures throughout  the  year  (p.  102).  As  we  have  seen,  this  results 
in  a  dense,  varied  vegetation  (Fig.  238),  like  the  forests  of  the  Amazon 
and  Congo  valleys.  The  distinctive  life  of  humid  plains  in  low  lati- 
tudes is  therefore  that  of  the  tropical  forest,  or  jungle.  In  some  of  the 
other  realms  which  we  have  considered,  man  has  been  handicapped 
by  lack  of  useful  vegetation.  Here,  the  very  abundance  of  plant  life 
is  an  obstacle  to  progress. 

Response  of  natives  to  conditions  in  tropical  forests.  The 
dense  forests  of  equatorial  regions  are  occupied  by  sparse  populations 
of  backward  natives.  The  high  temperatures  and  the  moisture  are 
enervating,  and  steady  work  is  difficult.  The  luxuriance  of  the 
natural  vegetation  makes  the  clearing  of  land  difficult,  and  after  it 
is  cleared,  a  constant  struggle  is  necessary  to  keep  out  the  plants  which 
are  not  wanted.  Unused  trails  through  the  forest  are  overgrown 
quickly,  and  all  trace  of  settlement  soon  disappears  from  abandoned 
clearings.  Under  these  conditions,  it  is  not  strange  that  agriculture 
rarely  is  practiced.  Throughout  the  world,  man  appears,  as  a  rule, 
to  have  developed  agriculture,  or  to  have  domesticated  animals, 
only  when  the  natural  food  supply  became  too  small.  In  the  equa- 
torial forest,  the  natural  food  supply  is  abundant.     The  natives  live 


338 


LIFE  IN  PLAINS 


chiefly  on  the  fish  afiforded  by  the  many  rivers,  and  such  game  as 
inhabits  the  forest.  This  is  supplemented  in  many  places  by  the 
products  of  certain  forest  plants,  such  as  the  sago  palm. 

The  large  animals  found  in  many  places  in  the  open  country  near  the  tropical 
forests  go  into  the  latter  only  a  short  distance.  They  come  and  go  through  the 
denser  growth  by  paths  which  they  keep  open  by  frequent  passing.  In  the  heart 
of  the  forest,  there  are  few  sources  of  food  for  animals  near  the  ground.  Flowers 
and  fruits  are  found  in  the  tree  tops,  however,  and  hence  animal  life  is  represented 


Fig.  238.  Tropical  forest  and  river  in  flood.  Southern  Mexico.  (W.  L. 
Tower.) 

chiefly  by  flying  and  climbing  forms,  such  as  insects,  birds,  snakes,  and  monkeys. 
Many  of  the  birds  and  snakes  resemble  the  foliage  in  color,  a  fact  which  favoiE 
concealment. 

Little  is  needed  by  the  inhabitants  of  the  tropical  forest  in  the 
way  of  clothing  and  shelter.  Some  of  the  lowest  savages  have  no 
homes.  Some  of  the  people  live  in  floating  houses  on  the  rivers,  o'' 
in  huts  built  on  piles  to  escape  the  floods.  Rivers  are  the  most  im- 
portant lines  of  travel  through  the  forest. 

A  little  farming  is  done  in  clearings  near  the  edges  of  the  equatorial 
forests.     In  some  cases,  this  consists  in  scarcely  more  than  planting 


PYGMIES  OF  THE  CONGO  FOREST 


339 


crops,  and  leaving  them  to  grow.  Bananas,  bread  fruit,  rice,  and  other 
things  are  grown  in  different  places,  chiefly  by  the  women.  Very 
little  labor  brings  large  returns,  so  that  steady  effort  is  discouraged. 
As  in  the  equatorial  forest  generally,  life  is  too  easy;  there  is  no  spur 
to  progress. 

The  Pygmies  who  live  in  parts  of  the  Congo  forest  are  perhaps  the  lowest  type 
of  human  beings.  Most  of  the  adults  are  only  a  little  more  than  4  feet  tall,  and 
many  are  shorter.  They  make  no  attempt  at  farming,  but  live  by  hunting  and 
fishing.  They  kill  small  game  with  arrows  and  spears  tipped  with  a  poison  made 
irom  certain  plants,  and  capture  even  large  animals  in  covered  pitfalls  which  they 


Fig.  239.     Pygmy  village  in  the  Congo  forest. 


make  in  the  narrow  runways  followed  by  the  animals  (p.  338).  They  catch  fish 
in  nets  or  baskets.  They  live  in  small,  scattered  groups  where  there  are  openings 
in  the  undergrowth  (Fig.  239),  building  temporary  huts  consisting  in  many  cases  of 
flexible  sticks  covered  with  leaves,  and  shifting  from  spot  to  spot  in  quest  of  game. 
They  carry  on  some  trade  with  other  tribes,  bartering  meat,  skins,  and  plant 
poisons,  for  weapons  and  vegetable  food.  The  Pygmies  have  no  arts  save  those 
connected  with  their  hunting  and  fishing,  and  no  family  ties. 

Commerce  of  tropical  forests.  The  forests  of  tropical  low- 
lands furnish  products  of  much  importance  to  the  outside  world, 
such  as  ebony,  mahogany,  rubber,  gums,  palm-oil,  and  copra.  Trade 
follows  the  waterways,  and  in  general  those  sections  are  most  favored 
commercially  which  are  situated  conveniently  with  reference  to  a 
navigable  river  (p.  104). 


340  LIFE  IN  PLAINS 

The  humid  lowlands  of  the  tropics  are  of  far  greater  importance 
to  man  than  the  Arctic  plains,  but  unfortunately  the  settlement  and 
development  of  them  by  people  from  middle  latitudes  are  attended 
with  great  difficulty  (pp.  loo,  103-104). 


Questions 

1.  How  might  one  prove  that  a  given  coastal  plain  was  formerly  a  marginal 
sea-bottom? 

2.  By  what  are  the  characteristics  (topography,  fertility,  etc.)  of  any  given 
plain  determined? 

3.  Why  are  the  soils  of  most  plains  thicker  and  more  fertile  than  those  of 
plateaus  and  mountains? 

4.  (i)  What  great  plains,  now  of  little  value  to  man,  are  hkely  to  have  greatly 
increased  importance  in  the  futiure?  Why?  (2)  What  ones  are  likely  to  continue 
of  little  significance?     Why? 

5 .  Compare  and  contrast  the  life  of  primitive  peoples  in  arid  deserts  and  rugged 
mountains. 

6.  How  does  the  life  of  people  in  Arctic  regions  resemble  that  of  desert  tribes 
in  lower  latitudes? 


CHAPTER  XIX 
COAST-LINES  AND   HARBORS 

Importance  of  coast-lines.  There  is  great  freedom  of  move' 
ment  over  the  ocean.  A  ship  may  sail  direct  from  one  port  to  another 
thousands  of  miles  away,  or  it  may  make  a  roundabout  voyage,  call- 
ing at  many  ports  on  the  way.  A  modern  steamship  can  carry  ten 
to  twenty  train  loads  of  freight  in  a  single  cargo,  and  it  costs  far  less 
to  operate  one  steamer  than  to  run  ten  or  twenty  trains.  Furthermore, 
trains  call  for  the  maintenance  of  a  railway,  which  is  very  expensive. 
Hence  the  carriage  of  freight  by  rail  is  much  more  costly  than  by  boat. 
Modern  commerce,  therefore,  depends  much  on  the  ocean  highway, 
but  it  owes  its  rapid  growth  in  part  to  favorable  coast-lines  through 
which  access  to  the  sea  is  secured. 

In  early  days,  seamanship  was  much  influenced  by  the  character 
of  the  coast-line.  It  was  unsafe  to  go  far  from  land,  for  vessels  were 
small  and  there  was  no  way  of  determining  position  accurately,  or 
of  reckoning  distances.  Hence  seamanship  developed  first  along 
the  shores  of  quiet  inland  seas  like  the  Mediterranean,  or  where  long 
bays  and  sheltering  islands  invited  ventures  from  one  headland  or 
island  to  another,  as  in  Norway.  Thus  the  first  nations  to  become 
sailors,  fishermen,  explorers,  and  sea  traders  were  influenced  by  the 
nature  of  their  sea-coasts. 

With  modern  steamships  and  skillful  seamen,  voyages  are  under- 
taken readily  to  distant  parts  of  the  earth.  But  even  the  giant  steam- 
ship needs  safe  anchorage  in  quiet  waters  while  its  cargo  is  being  load- 
ed or  unloaded.  Some  ocean  commerce  is  carried  on  from  places 
which  have  no  harbor,  but  in  such  cases,  vessels  anchor  off  shore  while 
the  cargo  is  carried  {lightered)  from  them  to  shore,  or  from  shore  to 
them,  in  small  boats.  During  heavy  seas  lightering  is  impossible, 
and  many  wares  cannot  be  handled  to  advantage  in  this  way  at  any 
time. 

Characteristics  of  coast-lines  and  their  origin.  If  land  along 
a  coast  were  to  be  elevated  or  the  sea-level  lowered,  a  portion  of 

341    . 


342 


COAST-LINES  AND  HARBORS 


the  sea  floor  would  be  exposed.  Most  of  the  sea  floor  is  smooth 
and  even.  Hence  the  emergence  of  a  coastal  strip  tends  to  make 
an  even,  regular  shore-line  (Fig.  240)  fronted  by  shallow  water. 
Coasts  which  have  risen  recently,  relative  to  sea-level,  are  without 
good  harbors,  except  where  some  large  river,  flowing  across  the 
coastal  plain,  offers  a  haven  at  its  mouth.  Commerce  with  such  a 
coast  is  at  a  disadvantage.  Large  vessels  must  anchor  off  shore  while 
their  cargoes  are  lightered,  unless  artificial  harbors  have  been  made  by 


Fig.  240.  Map  showing  regular  outline  of  a  newly  elevated  coast.  Dotted 
lines  indicate  contours;  interval  25  feet.  (Nome,  Alaska,  Special  Sheet,  U.  S. 
Geol.  Surv.) 


building  breakwaters,  jetties,  or  long  quays.  The  east  coast  of 
India  and  most  of  the  Gulf  coast  of  Mexico  present  these  conditions. 
Madras  and  Vera  Cruz  have  artificial  harbors  because  the  trade  from 
an  important  region  justified  the  great  expense  involved  in  making 
a  harbor. 

The  submergence  of  a  coast  land  having  hills  and  valleys  pro- 
duces a  new  shore-line  which  is  irregular,  the  drowned  valleys  form- 
ing bays  (Fig.  241).  Isolated  hills  on  the  old  lowlands  may  front  the 
new  coast  as  islands.  The  coast  of  Maine  furnishes  good  examples. 
Such  a  coast-line  commonly  has  many  sheltered  bays  and  harbors. 
Commerce  is  favored  by  such  a  coast.  Most  important  commercial 
ports,  such  as  the  Atlantic  ports  of  North  America  and  Europe,  are 
along  depressed  coasts.  The  chief  sea  fisheries,  also,  are  connected 
with  irregular  coasts,  partly  because  of  the  many  convenient  refuges 


EMBAYED   COAST-LINES 


343 


for  fishing  fleets.     Not  infrequently,  also,  large  bays,  like  Chesapeake 
Bay,  support  valuable  fisheries. 

Where  an  irregular  coast-line  is  produced  by  the  sinking  of  a  coastal  plain, 
the  bays  may  be  wide  (Why?),  like  Delaware  and  Chesapeake  bays,  but  most  of 
them  are  shallow,  except  along  the  line  of  the  old  river  channel,  and  they  may  have 
marshy  land  along  their  borders.  Few  places  on  the  shores  of  such  bays  are 
suitable  for  the  development  of  a  great  port.     Where  a  higher,  more  rugged  region 


Fig.  241.     Map  showing  irregular  outline  of  a  depressed  coast.     Dotted  lines 
indicate  contours;  interval  20  feet.  (Monhegan,  Maine,  Sheet,  U.  S.  Geol.  Surv.) 


is  submerged,  the  bays  are  likely  to  be  narrow  and  fiord-like,  as  in  Alaska  and 
Norway.  Most  of  them  are  deep,  and  some  are  bordered  by  high  land  which  rises 
so  abruptly  from  the  water  that  there  is  no  room  for  a  city. 

Where  the  ocean  finds  access  to  an  interior  valley,  a  long  inland  arm  of  the  sea, 
like  Puget  Sound,  is  developed.  A  former  mountain  pass  in  the  Coast  Range,  now 
submerged,  forms  the  picturesque  Golden  Gate  entrance  to  San  Francisco  harbor 
(Fig.  242),  and  a  little  further  sinking  would  change  much  of  the  central  valley  of 
California  into  a  great  sound. 

Changes  in  shore-lines.  Shore-lines  are  subject  to  constant 
change  by  waves,  shore  and  tidal  currents,  rivers,  winds,  and  ice. 


344 


COAST-LINES  AND  HARBORS 


The  effect  of  glaciers  on  shore-lines  has  been  noted  (pp.  256,  261). 
Much  of  the  value  of  Boston  harbor  depends  on  the  protection 
afforded  by  islands  of  glacial  origin.  Shore  ice  has  little  effect  on 
coast-lines,  but  hinders  navigation  along  some  coasts  (p.  246). 

Winds  often  make  dunes  on  the  sea  shore  (p.  202),  and  the  dunes 
may  afford  the  land  some  protection  from  the  sea,  as  along  the  coast 


Fig.  242.  Diagram  showing  arm  of  ocean  formed  by  invasion  of  valley  through 
a  submerged  sag  in  mountain  range.  San  Francisco  harbor.  Dotted  lines  indi- 
cate bar  across  entrance.    (U.  S.  Coast  and  Geod.  Surv.,  Chart  No.  5500.) 


of  Holland,  but  they  rarely  change  the  outline  of  the  land  to  any 
great  extent. 

Rivers  affect  shore-lines  little  by  erosion,  but  delta-building 
rivers  may  change  them  greatly  (p.  241).  Other  things  equal,  delta 
lands  grow  most  rapidly  in  the  quiet  waters  of  bays  and  inland  seas. 
Thus  the  delta  of  the  Mississippi  (Fig.  159)  extends  into  the  Gulf  as 
a  great  irregularity,  with  many  smaller  irregularities  about  its  borders. 
Delta-building  in  bays  may  lessen  the  irregularities  of  the  coast  by 
fiUing  the  bays.  The  value  of  Mobile  Bay  as  a  harbor  is  lessened 
because  of  the  sediment  deposited  in  it,  and  many  others,  which  were 
important  ports  centuries  ago,  are  now  partly  or  entirely  filled.     The 


WAVES  AND  SHORE  CURRENTS 


345 


city  of  Adria,  Italy,  once  the  port  for  the  mouth  of  the  Po,  is  now 
fourteen  miles  from  the  coast,  and  the  Rhone  delta,  building  forward 
at  the  rate  of  200  feet  a  year,  has  never  developed  an  important  port 
(p.  270). 

On  exposed  coasts,  delta-building  is  less  rapid  (Why?),  and  pro- 
duces fewer  irregularities.  The  delta  of  the  Amazon,  for  example, 
does  not  project  be- 
yond the  general  coast- 
line. Delta  lands  are 
low,  marshy,  and  sub- 
ject to  floods,  while 
the  bays  about  their 
borders  are  shallow. 
For  these  reasons  del- 
tas are  poorly  suited  to 
the  development  of 
ports,  and  except  at  the 
mouths  of  great  rivers, 
like  the  Mississippi, 
deltas  rarely  become 
the  sites  of  great  com- 
mercial cities. 

Waves  are  the  chief 
agent  changing  coast- 
lines. On  irregular 
coasts,  the  general  tend- 
ency of  waves  is  to  wear  away  headlands  (Fig.  243)  and  fill  bays, 
thus  making  the  shore  more  regular.  On  regular  coasts,  their  gen- 
eral tendency  is  to  wear  back  the  shore-line.  Waves  therefore  tend 
to  destroy  harbors.  In  many  cases  serious  harm  to  commerce  is 
prevented  only  by  costly  structures  built  to  protect  and  improve 
harbors. 

Waves  are  at  work  almost  constantly  on  some  part  of  every 
coast-line.  Large  waves  are  more  powerful  than  small  ones;  hence 
coasts  exposed  to  stormy  seas  are  worn  most,  and  those  of  loose 
material,  such  as  gravel  and  sand,  are  cut  back  more  than  those  of 
solid  rock.  The  gravel,  sand,  and  clay  of  the  Atlantic  Coastal  Plain, 
and  the  glacial  drift  of  parts  of  New  England,  are  washed  away  more 
readily  than  the  solid  rocks  of  Maine  or  Norway. 

In  deep  water  away  from  shore,  the  water  in  a  wave  does  not  move 


243.    Wave  erosion  of  an  exposed  headland. 


346 


COAST- LINES  AND  HARBORS 


forward.  An  idea  of  its  motion  may  be  gained  from  a  field  of  waving 
grain,  where  wave  after  wave  crosses  the  field,  though  each  moving 
stem  is  fixed  to  the  ground.  But  when  a  wave  advances  into  shallow 
water,  its  motion  changes  because  the  lower  part  of  the  wave  drags 
bottom,  and  so  is  made  to  go  more  slowly.  The  top  tends  to  pitch 
forward,  making  surf  (Fig.  244).  A  somewhat  similar  effect  may  be 
produced  in  deep  water  when  winds  blow  the  tops  of  waves  forward, 
forming  whitecaps.     Hence  during  storms,  and  especially  in  shallow 


Fig.  244.      Surf  wave  at  Point  Buchon,  California. 


water,  there  may  be  a  distinct  forward  movement  of  the  water  in  a 
wave,  but  generally  in  deep  water  it  is  only  the  wave  motion,  not 
the  water,  which  travels  forward. 

In  shallow  water,  the  water  which  is  thrown  forward  against 
the  shore  runs  back  down  the  slope  of  the  bottom  as  the  undertow. 
Drownings  have  resulted  so  frequently  from  bathers  being  caught  by 
the  undertow  that  many  bathing  beaches  now  have  regular  life  guards 
constantly  on  watch  during  bathing  hours. 

If  waves  reach  the  shore  obliquely,  they  produce  a  movement 
of  water  parallel  to  it.  Such  a  movement  is  known  as  a  shore  or 
littoral  current.  Where  a  shore  is  exposed  to  winds  prevailingly  from 
one  quarter,  the  resulting  shore  currents  are  somewhat  constant 
in  direction.  Littoral  currents  are  most  important  in  moving  the 
material  worn  from  the  land  by  waves. 


CLIFFS  AND   TERRACES 


347 


Fig.  245.  A  cliff  fronted  by  a  terrace. 
Outer  (dotted)  part  of  terrace  built  by 
deposition  of  sediment;  inner  part  due 
to  wave  cutting. 


Erosion  by  waves.  The  force  of  waves  hurled  against  the 
shore  may  be  very  great.  Surf  has  been  thrown  to  heights  of  more 
than  100  feet  with  force  enough  to  destroy  Hghthouses.  The  strength 
of  waves  on  the  coast  of  Great  Britain  is  sometimes  as  much  as 
three  tons  per  square  foot.  Such  waves  are  able  to  move  masses 
of  rock  weighing  several  tons. 
During  one  storm  more  than 
200  blocks  of  concrete,  weighing 
4  tons  each,  were  swept  from 
the  break-water  at  Cherbourg, 
France,  and  tossed  over  an  em- 
bankment. It  is  clear,  there- 
fore, that  the  force  of  waves  is 
great  enough  to  wear  shores, 
even  of  solid  rock.  Where  deep 
water  is  found  near  shore,  as 
along  most  steep  coasts,  erosion  depends  on  the  work  of  the  water 
alone.  Where  waves  break  in  shallow  water,  pieces  of  rock  may  be 
hurled  forward  with  the  rushing  water,  and  serve  as  powerful  tools  to 
cut  away  the  land.  In  severe  storms,  the  land  is,  in  rare  cases,  driven 
back  many  feet  in  a  few  hours.  The  waves  of  lakes  are  never  so  strong 
as  the  great  waves  of  the  sea  (Why?),  but  the  storm  waves  of  large  lakes 
have  great  force,  and  may  do  much  damage  even  in  a  single  storm. 

The  great  force  of  waves  on  an  exposed  coast  has  led  to  many 
attempts  in  different  countries  to  use  wave  power  for  industrial 
purposes.  None  of  the 
devices  yet  tried  has 
proved  practicable  on 
an  important  scale. 
One  obstacle  is  the  ex- 
tremely variable  char- 
acter of  the  waves. 

Where  waves  erode 
the  land  they  make 
steep  slopes,  or  clifs. 
Such  cliffs  are  bordered 

by  wave-cut  terraces  a  little  below  the  surface  of  the  water  (Fig.  245). 
The  width  of  such  a  terrace  measures  roughly  the  advance  of  the 
water  on  the  land  by  the  cutting  of  its  waves.  By  rise  of  the  land, 
or  by  sinking  of  the  sea,  the  terrace  may  become  land  (Fig.  246). 


246.     Wave-cut  terraces  now  well  above 


the  sea,  indicating  relative  change  in  level  of  land 
and  sea.    Seward  Peninsula,  Alaska. 


34S 


COAST-LINES  AND  HARBORS 


Fig.  247.    Wave-cut  cliff  with  some  of  the  mate- 


By  driving  back  sea  cliffs,  waves  tend  to  increase  the  area  of  the  sea 
at  the  expense  of  the  land.  The  island  of  Heligoland,  off  the  German 
coast,  has  been  so  worn  by  waves  that  it  is  less  than  one-twentieth 
as  large  as  it  was  a  thousand  years  ago.     Many  shoal  areas  off  the 

New  England  coast  are 
due  to  the  cutting 
away  of  small  islands. 
Deposition  by 
waves  and  shore  cur- 
rents. Material  worn 
from  the  land  by  waves, 
or  brought  to  the  shore 
by  rivers,  is  shifted 
about  by  waves,  under- 
tow, and  shore  cur- 
rents, but  finally  comes 
to  rest.  If  left  at  the 
shore-line  it  makes  a 
heach  (Fig.  247).  If 
carried  farther  out  into 
the  water,  it  takes  on 
other  forms.  Fine  par- 
ticles of  mud  generally  are  carried  out  into  deeper  water,  while 
coarser  material,  such  as  sand  and  gravel,  make  the  beach. 

Waves  may  build  reefs  or  barriers  a  little  way  out  from  the  shore. 
They  are  formed  near  the  line  of  breakers,  where  the  incoming  wave 
leaves  much  of  the  sediment  which  it  is  moving  toward  the  land. 
The  undertow  may  add  to  the  reef  by  carrying  sediment  out  from 
the  shore.      Some  reefs  are  troublesome    to  navigation,  especially 

where  they  make  "a  bar"  at 
the  entrance  to  a  harbor. 

Waves  may  build  the  crest 
of  a  reef  above  water,  convert- 
ing it  into  land  (Fig.  248).  By 
building  dunes,  the  wind  may 
then  aid  in  raising  the  surface  still  higher.  This  seems  to  have 
been  the  origin  of  many  low,  narrow  belts  of  sandy  land  parallel 
to  coasts,  with  marshes  and  lagoons  behind  them.  Such  barriers 
are  common  in  shallow  water,  as  at  many  places  from  New  York  to 
Texas.    Lagoons  behind  reefs  provide  harbors  in  some  places. 


rial  left  in  the  form  of  a  beach  at  its  base. 
Michigan. 


Lake 


Fig.  248.     Diagram    representing 
cross-section  of  a  barrier  beach. 


REEFS,  SPITS,  AND  BARS 


349 


Where  a  shore  current  reaches  a  bay,  it  does  not,  as  a  rule,  follow 
the  outline  of  the  bay,  but  tends  to  cross  it  in  the  direction  in  which 
it  had  been  moving.  Un- 
der such  circumstances  it 
may  build  an  embankment 
or  spit  of  gravel  and  sand 
near  the  entrance  to  the 
bay.  Currents  do  not 
build  spits  above  the  water, 
but  waves  may  build  them 
up  into  land  by  washing 
material  from  their  slopes 
up  to  their  tops.  After  they 
become  land,  the  wind  may 
build  dunes  on  them  (Fig. 
251).  When  spits  (Fig. 
249)  cross  bays  they  be- 
come bars.  Along  some 
coasts,  as  on  the  south  side 
of  Martha's  Vineyard  Is- 
land, such  bars  have  closed 
the  entrances  to  many  bays. 

Reefs,    spits,    and    the 
land   to  which   they  give 


Fig.  249.  Map  of  harbor  formed  by  spits; 
Plymouth,  Mass.  Broken  lines  show  ap- 
proximate limits  of  channel.  (U.  S.  Coast  and 
Geod.  Surv.,  Chart  No.  no.) 


rise,  increase  the  irregularity  of  the  coast-line  for  a  time;  but  they 
represent  the  first  step  toward  regularity,  for,  after  the  reefs  have 


."^.mll. 


Fig.  250.     A  barrier  beach  with  marshy  tract  (filled  lagoon)  behind  it.    La^- 
sells  Island,  Penobscot  Bay,  Me. 

become  land,  the  lagoons  behind  them  are  likely  to  be  filled  with  sedi- 
ment washed  down  from  the  land  or  blown  in  by  the  wind  (Fig.  250). 


350 


COAST-LINES   AND    HARBORS 


Deposits  of  gravel  and  sand  may  be  made  between  a  mainland  and 
islands  near  it.  The  Rock  of  Gibraltar,  on  the  coast  of  Spain,  has 
been  thus  "tied"  to  the  mainland. 

Bars  and  reefs  may  hinder  the  movements  of  vessels,  especially 
where  they  tend  to  close  the  entrances  of  harbors.  A  spit  which  does 
not  obstruct  the  entrance  to  a  harbor  is  sometimes  an  advantage,  since 
it  breaks  the  force  of  incoming  waves.    Spits  which  form  harbors  have 

determined  the  location 
of  numerous  villages  and 
cities.  The  harbor  of  Pl>Tn- 
outh,  Mass.,  for  example, 
is  protected  by  a  spit  which 
makes  a  natural  break- 
water (Fig.  249).  Prov- 
incetown,  Mass.,  and  Erie, 
Penn.  (Fig.  251),  have  har- 
bors made  by  curved  spits. 
Harbors.  Harbors  vary 
greatly  in  value.  A  good 
harbor  must,  first  of  all, 
afford  shelter  from  stormy 
seas,  must  be  deep  enough 
for  large  vessels,  must  be 
connected  with  the  open 
ocean  by  a  deep  channel, 
and  must  provide  room  for 
many  ships.  ^  The  direction  whence  the  storm  waves  come  and  the 
direction  which  the  harbor  entrance  faces  have  much  to  do  with  its 
safety.  A  harbor  with  a  wide,  unprotected  entrance,  facing  the 
south,  may  be  a  good  haven  on  a  coast  where  the  storm  waves  come 
from  the  east  or  northeast.  The  harbor  of  Gloucester  (Mass.)  illus- 
trates this  condition.  The  straighter  and  wider  the  channel  leading 
mto  the  harbor,  the  better,  for  long  vessels  cannot  navigate  safely  a 
narrow,  winding  channel.  This  fact  alone  made  it  necessarv  to  open 
a  new  entrance  (Ambrose  channel)  to  New  York  harbor.  The  water 
near  the  shore  should  be  deep  enough  to  permit  vessels  to  reach  the 
docks,  and  the  shore  should  be  suitable  for  landings  and  port  facilities. 
A  good  harbor  should  be  free  from  ice. 

A  harbor  may  have  all  these  qualifications  and  yet  be  of  little  value 
commercially.    Thus  Casco  Bay,  Maine,  is  said  to  be  one  of  the  finest 


Fig.  251.  Map  of  harbor  formed  by  curved 
spit,  Erie,  Penn.  Dotted  areas  are  lines  of 
sand  dunes.  (Erie,  Penn.,  Sheet,  U.  S.  Geol. 
Surv.) 


REQUIREMENTS   OF   GOOD   HARBORS  351 

havens  in  the  world,  but  Portland  is  one  of  the  lesser  Atlantic  ports. 
For  commercial  importance  (Figs.  252  and  253),  a  harbor  must  have 
good  Hnes  of  transportation  either  to  a  large  producing  region,  or  to 
one  which  requires  many  wares  from  the  outside  world.  Thus  New 
York  is  first  among  Atlantic  ports,  not  so  much  because  of  a  better 
harbor,  as  because  of  its  better  connections  with  the  interior,  where 
many  articles  of  commerce  are  produced  and  consumed.  As  a  whole, 
the  Pacific  coast  of  the  United  States  is  less  important  commercially 
than  the  Atlantic  coast,  partly  because  of  the  broad  deserts  and  high 
mountains  which  he  behind  it  (p.  401). 

Harbors  at  the  mouths  of  large  rivers  are  likely  to  have  easy 
communication  with  the  interior  through  river  na\dgation,  and  the 
valleys  are  natural  routes  for  railways.  Thus  important  ports,  hke 
New  Orleans  (Figs.  252  and  253),  Para,  Calcutta,  and  Rangoon,  are 
near  the  mouths  of  rivers  which  serve  as  highways  of  trade.  River- 
mouth  harbors,  however,  have  many  disadvantages.  The  current 
is  a  handicap  for  sailing  vessels,  which  are  still  important  in  coast- 
wise commerce.  Many  large  rivers,  like  the  Mississippi,  Amazon, 
and  Ganges,  have  large  deltas,  on  which  the  stream  breaks  up  into 
distributaries,  whose  mouths  may  be  blocked  by  deposits  of  silt  and 
mud.  Shallow  water  is  common  near  the  entrances,  and  this  disad- 
vantage increases  as  larger  vessels  are  built.  Not  infrequently  the 
main  discharge  of  the  stream  shifts  from  one  mouth  to  another. 
In  many  rivers  winding  channels  are  kept  open  only  by  building 
jetties  to  direct  the  current. 

For  these  reasons  expensive  work  has  been  undertaken  in  some  cases,  such  as 
the  building  of  the  Eads  jetties  at  the  Southwest  Pass  from  the  Mississippi,  in  order 
to  keep  one  mouth  open  and  deep  at  all  times.  In  other  cases,  the  port  developing 
in  connection  with  a  river  has  been  located  at  the  nearest  favorable  place,  free  from 
the  disadvantages  of  the  river  mouth.  Thus  iSIarseilles  is  about  30  miles  from  the 
mouth  of  the  Rhone,  and  Kurachi  is  some  15  miles  from  the  mouth  of  the  Indus. 
In  each  case,  connection  with  the  river,  inland,  is  made  by  rail. 

Most  of  the  important  harbors  of  the  world  have  been  made 
by  the  submergence  of  river  valleys.  The  harbors  of  New  York, 
Philadelphia,  San  Francisco,  Seattle,  Liverpool,  London,  Ham- 
burg, Shanghai,  and  hundreds  of  others  belong  to  this  class.  The 
embayed  river  has  many  advantages  over  such  a  stream  as  the  Ama= 
zon,  as  the  place  for  a  commercial  center.  The  entrance  rarely  shifts, 
is  likely  to  be  deep,  and  not  infrequently  tidal  currents  prevent  its 
being  filled  by  sediment.     Water  navigation  also  may  be  possible 


352 


COAST-LINES  AND  HARBORS 


Fig.  252.  Diagram  showing  movement  of  exports  from  the  United  States  by 
coasts  and  leading  ports,  1910.  Values  are  expressed  in  millions  of  dollars.  Per- 
centages refer  to  proportion  of  total  trade. 


Fig.  253.  Diagram  showing  movement  of  imports  into  the  United  States  by 
coasts  and  leading  ports,  1910.  Values  are  expressed  in  millions  of  dollars.  Per- 
centages refer  to  proportion  of  total  trade. 


HARBORS  AND   COMMERCE 


353 


for  some  distance  inland.  Thus  boats  can  go  from  Shanghai  far 
into  the  interior  of  China  (p.  269),  and  Hamburg  benefits  from 
a  water  route  which  reaches  the  Aus- 
trian frontier. 

Many  harbors  on  embayed  coasts  are  af- 
fected by  the  deposition  of  sediment  in  or  across 
their  entrances  (Fig.  254).  The  direction  in 
which  the  entrance  opens,  with  respect  to  the 
movement  of  shore  currents,  is  important  in  this 
connection.  Thus  the  embayed  mouth  of  the 
Housatonic  River  receives  the  material  drifted 
westward  by  the  shore  currents  of  Long  Island 
Soimd.  As  a  result  its  entrance  is  very  shallow, 
and  the  river  mouth  has  no  important  port. 
New  Haven  harbor,  on  the  other  hand,  is  so  sit- 
uated that  the  shore  current  is  turned  away  from 
the  entrance  toward  deeper  water.  Its  entrance 
is  deep  enough  for  the  passage  of  good-sized 
vessels,  and  partly  for  this  reason  New  Haven 
early  became  an  important  shipping  center.  On 
some  coasts  where  harbors  occur  only  at  rather 
long  intervals,  jetties  have  been  built  to  over- 
come the  action  of  shore  currents  (Fig.  255). 
Galveston  harbor  has  been  improved  in  this  way. 

Fiords  are  numerous  along  some 
coasts,  but  they  are  relatively  unimpor- 
tant as  sites  for  large  ports,  partly 
because  many  fiords  are  in  high  lati- 
tudes where  commerce  is  not  very 
important,  and  partly  because  of  the 
character  of  the  fiords  themselves. 
Many  are  too  deep  for  anchorage  in 
the  main  channel,  their  land  borders 
are  too  steep  and  high  for  the  growth 
of  a  large  port,  and  they  are  associated 
in  many  cases  with  mountains  which 
hamper  communication  with  the  interior 
(Fig.  176).  The  quiet  upper  waters  of 
fiords,  however,  afford  good  protection 
from  storm  waves,  and  every  primitive 
people  occupying  a  fiord  coast  early  developed  the  sea-going  habit. 

Lagoon  harbors  may  be  produced  by  the  formation  of  barriers,  or 
by  the  growth  of  coral  reefs.     The  former  are  numerous  along  the 


Fig.  254.  Map  of  river 
mouth  with  shallow  water  over 
the  bar  at  the  entrance;  Cal- 
casieu Pass,  La.  Dotted  lines 
indicate  6  foot  depth.  Broiien 
line  indicates  12  foot  depth. 
Figures  give  depth  in  feet.  The 
channel  across  the  bar  changes 
with  every  gale,  so  that  stran- 
gers are  warned  not  to  enter 
without  a  pilot.  (U.  S.  Coast 
and  Geod.Surv., Chart  No. 202.) 


354 


COAST-LINES  AND  HARBORS 


ANTUCI 


Atlantic  and  Gulf  coastal  plains,  but,  except  where  combined  with 
sunken  coast-lines,  few  attain  commercial  value.  The  water  off  shore 
is  rarely  deep,  most  of  the  inlets  are  narrow  and  shallow,  and  many- 
have  such  strong  tidal  currents  as  to  prevent  the  ready  passage  of 

small  craft.  The  inlets  also 
may  be  closed  by  sediments 
deposited  by  waves  and 
currents,  unless  protected 
by  artificial  works.  The 
lagoon,  even  if  deep  origin- 
ally, or  dredged  to  a  sat- 
isfactory depth,  tends  to 
become  shallower  through 
the  deposition  of  sediment. 
Most  lands  bordering  la- 
goons are  low  and  marshy 
on  the  mainland  side,  with 
only  a  low,  sandy  island,  ex- 
posed to  winds  and  waves, 
on  the  ocean  side.  Neither 
is  well  fitted  to  be  the  site 
of  a  great  port.  Galveston 
is  the  best  example  of  a 
port  with  a  lagoon  harbor; 
large  sums  have  been  spent 
to  develop  and  maintain 
both  the  harbor  and  the 
city.  Lagoon  harbors  due 
to  coral  reefs  or  atolls  are 
fairly  numerous  in  tropical 
waters,  especially  in  the 
South  Pacific,  but  are  of 
little  importance,  because  most  of  them  are  associated  with  small 
islands,  which  have  little  commerce.  The  Great  Barrier  Reef  of 
Australia  harms  rather  than  helps  the  commerce  of  that  country. 

Few  harbors  are  suited  naturally  to  all  the  demands  of  present-day  commerce. 
Crooked  channels  must  be  straightened,  and  narrow  and  shallow  channels  must  be 
dredged.  The  opening  of  the  Ambrose  channel  in  New  York  harbor  is  an  example. 
This  new  entrance  to  the  leading  Atlantic  port  of  the  United  States  involved  the 
improvement  of  an  old  channel  which  had  a  depth  of  only  i6  feet  at  low  tide. 


I^ANTUCKET 


Fig.  255.  Map  of  harbor  maintained  by 
jetties;  Nantucket,  Mass.  Broken  lines  indi- 
cate approximate  course  of  channel.  (U.  S. 
Coast  and  Geod.  Surv.,  Chart  No.  iii.) 


IMPROVEMENT   OF   HARBORS  355 

This  depth  was  enough  for  light-draft  vessels,  like  scows  and  towboats,  but  the 
need  for  a  better  entrance  led  to  the  deepening  and  widening  of  the  channel  so 
that  it  now  has  40  feet  of  water  at  low  tide,  and  a  width  of  2,000  feet  for  a  length 
of  seven  miles.  The  work  was  done  by  powerful  dredges  at  a  cost  of  about  six 
million  dollars.  In  a  single  year  more  than  600  trips  were  made  by  vessels  of 
such  size  that,  before  the  opening  of  the  new  channel,  they  could  have  entered 
only  by  lightering,  or  by  waiting  for  very  high  tide.  The  channel  from  Philadelphia 
to  the  sea  must  be  dredged  to  a  depth  of  35  feet  in  order  to  admit  the  largest  ocean 
vessels.  A  plan  is  on  foot  to  make  a  new  port  at  the  eastern  end  of  Long  Island, 
to  accommodate  steamers  having  such  a  length  that  docking  faciUties  are  no 
longer  convenient  in  the  Umited  space  along  the  New  York  water  front. 

In  many  places  the  demands  of  commerce  from  lands  bordered  by  regular 
coasts  compel  the  spending  of  large  sums  for  artificial  harbors.  Dover,  England, 
has  one  of  the  greatest  artificial  harbors  in  the  world.  There  a  series  of  concrete 
breakwaters  more  than  two  miles  long  enclose  a  harbor  of  nearly  one  square  mile, 
with  a  minimum  depth  of  40  feet.  The  harbor  cost  more  than  $20,000,000,  Its 
chief  value  is  as  a  base  for  naval  vessels  at  a  strategic  point  on  the  English  coast. 
A  breakwater  nearly  two  miles  long  has  been  built  at  Hilo,  Hawaii,  to  protect 
shipping  from  the  northeast  trades.  Similar  extensive  additions  have  been  made 
recently  to  the  works  at  Madras,  to  make  that  port  equal  to  the  other  commercial 
centers  of  India. 

To  keep  pace  with  the  ever-increasing  demands  of  commerce,  large  appropria- 
tions are  made  annually  by  our  federal  government.  From  the  standpoint  of 
commerce,  harbor  improvement  is  one  of  the  most  important  phases  of  govern- 
ment work. 

Many  ports  once  important  have  declined  because  of  the  changing 
conditions  of  commerce.  Thus  the  discovery  of  the  all-sea  route  to 
India  in  1497  shifted  the  main  scene  of  commerce  from  the  Mediter- 
ranean to  the  Atlantic  coast  of  Europe.  Mediterranean  ports,  like 
Venice,  declined  to  such  an  extent  that  they  almost  ceased  to  be 
factors  in  the  handUng  of  European  commerce.  The  opening  of  the 
Suez  Canal  (1869),  however,  made  the  Mediterranean  the  shortest 
route  for  trade  between  western  Europe  and  the  Orient;  it  led  to  a 
great  expansion  in  the  volume  of  commerce  between  those  regions, 
and  gave  a  new  stimulus  to  Mediterranean  ports. 

A  similar  condition  is  found  in  the  Caribbean  Sea  and  the  Gulf 
of  Mexico.  These  bodies  of  water  bear  to  the  Atlantic  and  the  Amer- 
icas a  relation  resembling  that  borne  by  the  Mediterranean  to  the 
same  ocean  and  the  continents  of  the  Old  World.  Here  also  a  narrow 
isthmus  blocks  communication  with  the  Pacific.  The  Panama  Canal, 
however,  will  open  this  route.  By  shortening  the  distance  from 
our  Atlantic  ports  to  most  Pacific  points,  it  will  make  the  Carib- 
bean a  more  important  highway,  and  lead  to  increase  of  trade  be- 
tween  the   two  oceans.     The  neighboring   ports,   like   those  along 


3S6  COAST-LINES  AND  HARBORS 

the  Gulf  coast  of  the  United  States,  will  be  stimulated  by  new  traf- 
fic, destined  for  Pacific  points;  they  are  also  likely  to  benefit  much 
as  handling  centers,  on  account  of  their  position  as  way-stations 
between  the  populous  countries  of  the  East  and  West.  Many  Pacific 
ports  will  be  benefited  similarly  by  freer  communication  with  the 
Atlantic. 

Questions 

1.  Why  is  Holland  better  situated  than  Belgium  for  carrying  on  sea  trade? 

2.  Why  are  the  natives  of  the  Malay  archipelago  expert  boatmen? 

3.  Why  is  the  location  of  Montreal  better  than  a  place  at  the  entrance  to  the 
Gulf  of  St.  Lawrence  for  the  development  of  a  seaport? 

4.  What  dangers  threaten  vessels  plying  along  submerged  coasts?  Along 
recently  elevated  coasts? 

5.  How  would  a  submergence  of  500  feet  affect  the  Mississippi  River  system? 

6.  How  can  the  direction  of  shore  currents  be  determined  from  the  outline 
of  the  coast?     Explain  in  the  case  of  Cape  Cod. 

7.  Why  are  there  few  important  commercial  centers  on  the  coast  between 
Cape  Henry  and  Cape  Florida? 

8.  What  prevents  Portland,  Me.,  from  being  a  leading  commercial  center? 
g.    Classify  the  leading  seaports  of  the  United  States  according  to  the  kinds 

of  harbors  which  they  possess. 

10.  Why  are  some  harbors  in  tropical  regions,  as  Manila  harbor,  well  pro- 
tected at  one  season  and  not  at  another? 

11.  Which  Gulf  ports  are  likely  to  benefit  most  from  the  opening  of  the 
Panama  Canal?     Why? 

12.  Why  would  fishing  villages  be  more  likely  to  develop  along  the  coast 
shown  in  Fig.  241,  than  along  that  shown  in  Fig.  240? 

13.  Suggest  the  probable  course  of  shore  currents  along  the  coasts  shown  ia 
Figs.  251  and  255.  Which  harbor  is  likely  to  be  affected  the  more  seriously  by 
shore  currents?     Why? 

14.  Suggest  reasons  why  New  York  is  a  great  exporting  and  importing  city, 
and  why  Galveston  exports  much  but  imports  little. 


CHAPTER   XX 

DISTRIBUTION   AND   DEVELOPMENT  OF  THE   LEADING  IN- 
DUSTRIES  OF  THE   UNITED   STATES 


Agriculture 

Importance  of  agriculture.  Agriculture  is  the  most  funda- 
mental industry  of  the  United  States;  it  furnishes,  directly  or  in- 
directly, most  of  what  we  eat  and  wear,  and  other  needs  are  less 
important  than  food  and  clothing.     More  than  }i  of  the  wage-earners 


Fig.  256.  Wage-earning  population  in  agricultural  pursuits  in  each  state  in 
1900  shown  by  inner  black  circle,  and  by  the  smaller  number  adjacent;  wage- 
earning  population  in  all  pursuits  shown  by  the  outer  ring,  and  by  the  larger 
number  adjacent.  Numbers  =  thousands  of  wage-earners.  (After  Middleton 
Smith.) 

of  the  country  are  engaged  in  agriculture  (Fig.  256).  The  total  value 
of  farm  lands  increased  about  H  between  1900  and  1905,  and  in  1910 
amounted  to  more  than  $28,000,000,000.  About  half  the  farm  lands, 
or  approximately  one-fourth  the  area  of  the  country,  is  cultivated. 

357 


358 


DISTRIBUTION  OF  INDUSTRIES 


Fig.  257  shows  the  relation  of  improved  acreage  to  total  farm  acreage 
(including  woodlots,  etc.)  in  the  different  states. 

The  total  value  of  all  farm  products  has  increased  each  year  for 
more  than  a  decade,  and  reached  nearly  $9,000,000,000  in   19 10. 


Fig.  257.    Map  showing  relation  of  improved  acreage  (black  circles)  to  total 
farm  acreage  (outer  rings)  in  the  different  states  in  1900.     The  smaller  numbers 
adjacent  to  the  circles  =  millions  of  acres  of  improved  land;  the  larger  numbers  = 
millions  of  acres  of  farm  land.     (After  Middleton  Smith.) 

This  was  more  than  double  the  figure  for  1900  (Fig.  258).     In  1910, 
the  six  crops  leading  in  value  were  corn,  cotton,  hay,  wheat,  oats, 


billions   of  Dollars 

1234S8T89 

1870  HIH^^^ 

1880  ■■■■■■■■ 

Fig.  258.     Diagram  showing  total  value  of  farm  products  in  the  United  States 
for  the  census  years  1 870-1910. 

and  potatoes.     The  United  States  produces  about  Vs  of  the  corn 
of  the  world,  Vs  of  the  cotton,  V4  of  the  oats,  and  Vs  of  the  wheat. 


IMPORTANCE  OF  CORN  CROP 


359 


The  leadership  of  the  United  States  in  agriculture  is  due  to  (i)  the 
extent,  variety,  and  high  average  fertility  of  its  soils;  (2)  the  favorable 
climate  of  most  sections,  with  range  sufficient  to  favor  the  produc- 
tion of  many  crops;  (3)  the  facilities  for  marketing  products;  (4)  the 
energy  and  ability  of  the  farming  people  as  a  whole;  and  (5)  the 
activity  of  federal  and  state  agencies  in  introducing  new  plants, 
better  seeds,  and  scientific  methods  of  cultivation. 

Leading  Crops 

The  general  distribution  of  crops  throughout  the  United  States  is 
controlled  largely  by  cHmate  (pp.  119,  121,  127,  131).  Their  detailed 
distribution  is  influenced  also  by  soil,  topography,  transportation 
facilities,  market  conditions,  and  other  factors.  It  is  practicable  to 
consider  here  only  the  leading  crops. 

Com.  Corn  is  our  most  important  crop  —  in  total  value, 
acreage,  and  amount  grown.     More  than  300  varieties  of  corn  are 


UNITED  STATES 

2.J84   MILLION 
BUSHLLS 


Fig.  259.  Average  annual  production  of  corn  in  the  different  states  (1899-1Q08). 
Figures  in  states  represent  production  in  millions  of  bushels.  (After  Middleton 
Smith.) 

known,  but  only  a  few  are  grown  in  large  amount.  The  leading 
varieties  thrive  best  where  there  are  plentiful  rains  with  prevailingly 
warm,  sunny  weather  during  the  growing  season,  and  in  rich,  well- 
drained  soils.     The  "corn  belt"  is  south  of  the  "wheat  belt,"  be- 


36o  DISTRIBUTION  OF  INDUSTRIES 

cause  the  staple  varieties  of  corn  require  a  higher  temperature  and 
a  longer  warm  season.  Illinois,  Iowa,  Nebraska,  Missouri,  Kansas, 
and  Indiana  are  the  leading  corn-producing  states  (Fig.  259).  The 
average  yield  of  corn  per  acre  is  about  25  bushels.  Experiments 
show  that  this  can  be  doubled  at  least  by  the  general  adoption  of 
better  methods  of  tillage,  careful  selection  of  seed,  and  the  use  of  vari- 
eties best  suited  to  the  places  in  which  they  are  grown.  During  the 
last  five  years  the  corn  crop  of  the  United  States  has  averaged  nearly 
2,700,000,000  bushels. 

Because  of  the  low  price  of  corn,  compared  to  its  bulk  and  weight, 
little  is  shipped  to  distant  markets.  Most  of  it  is  used  where  it  is 
grown,  to  feed  stock.  Corn  is  used  also  as  a  breadstuff,  and  in  the 
manufacture  of  whiskey  (p.  389),  glucose,  and  other  products. 

Corn  appears  to  be  a  native  of  the  highlands  of  Mexico,  whence  its  cultiva- 
tion spread  northward  and  southward  at  an  early  date.  The  colonists  found  it 
cultivated  more  or  less  by  many  of  the  Indians,  and  in  many  cases  they  promptly 
began  to  grow  it.  A  number  of  the  successful  English  settlements  of  eastern 
United  States  probably  would  have  failed  but  for  this  food  plant.  As  settlement 
spread  westward,  corn  was  the  staple  crop  of  much  of  the  frontier.  It  was  easy  to 
cultivate,  and  usually  returned  a  relatively  large  yield.  It  was  stored  easily, 
easily  prepared  for  food,  and  was  nourishing  both  for  animals  and  man.  "The 
progress  of  our  conquest  of  this  continent  would  have  been  relatively  slow  had 
it  not  been  for  the  good  fortune  which  put  this  admirable  food  plant  in  the  posses- 
sion of  our  people." 

Wheat.  In  the  United  States,  wheat  is  the  most  important 
food  plant.  It  probably  originated  and  was  cultivated  first  in 
Mesopotamia,  but  its  culture  spread  in  prehistoric  times  into  other 
parts  of  Asia,  and  into  Europe  and  North  Africa.  Its  great  value 
as  food,  the  comparative  ease  with  which  it  can  be  transported 
(Why?),  and  its  power  to  adjust  itself  to  new  conditions,  favored  its 
wide  and  rapid  dispersal.  As  a  result  of  long  cultivation  and  selec- 
tion under  different  conditions,  there  are  now  more  than  1,000  vari- 
eties of  wheat,  adapted  to  rather  diverse  conditions. 

Wheats  are  commonly  classified  as  spring  and  winter  wheat,  red,  white,  hard, 
and  soft.  In  the  northern  interior  states  spring  wheats  chiefly  are  grown,  for 
plants  from  seeds  sown  in  the  fall  are  "winter-killed";  farther  south,  much  winter 
wheat  is  raised.  In  general,  soft  wheats,  relatively  rich  in  starch,  are  used  in  mak- 
ing flour,  while  the  very  hard  kinds,  rich  in  gluten,  are  used  chiefly  for  the  manu- 
facture of  macaroni  (p.  1 28).  The  last  is  especially  true  of  the  durum  wheat  grown 
in  the  western  Great  Plains  (p.  173).  Hard  and  soft  varieties  are  commonly  mixed 
in  making  flour.     The  chief  white  wheat  district  is  in  the  Pacific  coast  states. 


THE  WHEAT  CROP 


361 


Fig.  260  shows  the  average  annual  production  (1899-1908) 
of  wheat  in  the  different  states.  The  total  wheat  crop  of  the 
country    in    191 1    (more    than    650,000,000    bushels)    was    nearly 


UNIILD  STATES 
640i  MILLION 
BUSHELS 


©1900 


Fig.  260.  Average  annual  production  of  wheat  in  the  different  states  (1899- 
1908).  Figures  in  states  represent  production  in  millions  of  bushels.  (After 
Middleton  Smith.) 

seven  times  as  great  as  that  of  1850.  This  increase  was  due 
to  (i)  the  demands  of  the  increasing  population,  (2)  the  occupa- 
tion of  new  areas  suited  to  wheat  culture,  (3)  the  improvement  and 
general  use  of  farm 
machinery,  and  (4)  the 
improved  conditions 
for  storing,  transport- 
ing, and  milling  the 
grain.  As  in  the  case 
of  most  other  crops, 
the  average  yield  per 
acre  of  wheat  in  the 
United  States  can  be 
increased  greatly.    For 


©1890 


O  CORN 

©WHEAT 

#OATS 


•1890 
©1880       ©1870    I 


^1900  OJ880 


Fig.  261.     Map  showing  centers  of  production 
of  corn,  wheat,  and  oats  (1850-1900). 


the  ten  years  1897  to  1906,  inclusive,  it  was  13.8  bushels;  during  the 
same  time  it  was  32.2  bushels  in  the  United  Kingdom,  28  in  Ger- 
many, and  19.8  in  France.     During  recent  years  the  exportation  of 


362 


DISTRIBUTION  OF  INDUSTRIES 


wheat  from  the  United  States  has  decreased,  as  the  demands  of  the 
home  market  have  increased.  While  the  acreage  devoted  to  wheat 
culture  in  the  United  States  can  be  increased  in  the  semi-arid  sections, 
and  wheat  may  be  imported,  the  greater  supply  needed  in  the  future 
must  be  obtained  chiefly  by  securing  larger  yields  where  wheat  is 
already  grown.  The  centers  of  cultivation  for  wheat  and  the  other 
leading  cereals  have  moved  steadily  westward  (Fig.  261). 

Other  cereals.  Oats  thrive  best  in  a  moist  and  relatively  cool 
climate.  They  do  fairly  well  in  some  of  the  southern  states,  where 
the  climate,  though  warm,  is  moist,  but  do  not  grow  well  where  it 


UNITED  STATES 
849  MILLION 
BUSHELS     " 


Fig.  262.  Average  annual  production  of  oats  in  the  different  states  (1899- 
1908).  Figures  in  states  represent  production  in  millions  of  bushels.  (After 
Middleton  Smith.) 

is  both  warm  and  dry.  The  chief  area  of  production  is  in  the  north- 
ern Interior  (Fig.  262).  In  recent  years  the  total  oats  crop  of  the 
country  has  averaged  nearly  a  billion  bushels.  A  small  part  of  the 
crop  is  used  as  food  for  man,  chiefly  in  the  form  of  oatmeal;  most 
of  it  is  used  as  feed  for  animals. 

Although  barley  can  be  grown  successfully  under  a  wider  range 
of  climatic  conditions  than  either  wheat  or  corn,  its  cultivation  in 
the  United  States  is  confined  largely  to  the  region  west  of  Lake 
Michigan  (from  Wisconsin  to  the  Dakotas),  and  to  the  Pacific  coast. 
In  the  order  of  their  importance,  the  leading  states  are  California, 


COTTON  CULTURE 


363 


Minnesota,  Wisconsin,  North  Dakota,  Iowa,  South  Dakota.  In 
the  northern  Interior  the  barley  is  used  chiefly  for  the  manufacture 
of  malt  liquor  (p.  389),  and  on  the  Pacific  coast  for  feed. 

Among  the  minor  cereals  grown  in  the  United  States  for  their 
grains  or  for  forage  are  rice  (Fig.  263),  rye,  buckwheat,  kaffir  corn, 
and  millet. 

Hay.  Hay  includes  various  grasses  and  legumes  which  are 
"cured"  as  food  for  stock.  The  more  important  ones  are  timothy, 
clover,  and  alfalfa  (p.  297).  Some  of  the  cereal  grasses,  like  oats  and 
barley,  sometimes  are  grown  for  hay.     Hay  is  produced  in  every 


V 

3CT" 

1 \ 

^ 

. 

936Z     i 

/ 

368992 

•    / 

1416032  \ 

9^ 

2\91 

• 

\6036\*/ 

^4 

0 

1 

V 

^ 

\  UNITED  STATES 

\  832,607  THOUSAND 
POUNDS 

Fig.  263.  Average  annual  production  of  rice  in  different  states  (1904-1908). 
Figures  represent  production  in  thousands  of  pounds.     (After  Middleton  Smith.) 

State,  but  the  chief  area  is  in  the  eastern  half  of  the  country,  north  of 
the  37th  parallel.  Although  alfalfa  is  cultivated  chiefly  in  the  western 
part  of  the  country,  it  probably  will  become  of  importance  in  the 
middle  states  in  the  near  future,  because  of  its  relatively  large  yields, 
its  high  nutritive  value,  and  its  importance  in  increasing  the  amount 
of  nitrogen  in  the  soil  (p.  29). 

Cotton.  The  cotton  of  commerce  is  the  fiber  which  surrounds 
the  seeds  of  the  cotton  plant.  The  value  of  the  fiber  and  the  uses 
to  which  it  is  put  depend  on  its  length  (jA  to  2}4  inches),  strength, 
fineness,  and  color.  The  cotton  plant  requires  a  warm,  moist  cUmate, 
and  a  relatively  long  season  free  from  frost.  These  are  the  principal 
factors  which  limit  the  cotton-producing  area  of  the  United  States  to 
the  southern  part,  east  of  the  Great  Plains  (Fig.  264).  In  some 
other  countries,  the  area  of  cotton  culture  may  be  extended.  Sea- 
island  cotton,  characterized  by  its  long,  fine  fiber,  thrives  best  on  cer- 
tain islands  off  the  South  Atlantic  coast,  partly  because  of  the  high 


364 


DISTRIBUTION  OF  INDUSTRIES 


humidity.  Sea-island  cotton  is  also  grown  some  distance  inland  in 
southern  Georgia  and  northern  Florida.  In  general,  the  largest 
yields  of  cotton  are  obtained  on  the  alluvial  soils  of  the  valley  bottoms, 
and  on  the  limey  soils  of  the  coastal  plain  (p.  171).  During  the  last 
five  years  the  total  cotton  crop  of  the  country  has  averaged  more 
than  12,000,000  bales.  About  Y^  of  the  cotton  grown  in  the  United 
States  is  manufactured  at  home  (p.  387) ;  the  rest  is  exported. 

The  cultivation  of  cotton  in  the  United  States  began  in  the  colonial  period, 
but  increased  slowly  until  after  the  invention  of  the  cotton  gin  (Eli  Whitney,  1792) 
in  this  country,  and  of  spinning  machinery  in  England.  The  former  made  easy 
the  separation  of  the  fiber  from  the  seed,  enabling  one  man  to  do  as  much  as  100 


UNITED  STATES 

10,848  THOUSAND 

BALES 


Fig.  264.  Average  annual  production  of  cotton  in  different  states  (1899-1908). 
Figures  represent  production  in  thousands  of  bales.  A  bale  is  400-500  pounds. 
(After  Middleton  Smith.) 

to  200  could  do  by  hand.  These  things,  coupled  for  some  years  with  unusually 
high  prices  for  cotton,  caused  a  great  increase  in  its  production.  The  develop- 
ment of  the  cotton  industry  meant  also  a  greatly  increased  demand  for  slaves  as 
field  hands.  The  work  in  the  cotton  fields  was  simple,  requiring^ little  skill  and  few 
tools.  In  these  and  other  ways  it  was  adapted  to  slave  labor,  and,  as  years  passed, 
cotton  culture  and  slavery  became  mutually  dependent.  They  became,  too, 
dominant  factors  in  the  economic,  social,  and  political  life  of  the  southeastern 
states,  and  helped  to  separate  their  interests  in  many  ways  from  those  of  the 
northern  states.  Thus,  the  New  England  cotton  manufacturer  (p.  387)  demanded 
a  tariff  on  imported  goods  to  protect  him  against  foreign  competition;  the  southern 
cotton  planter,  who  bought  many  of  his  supplies  abroad,  was  injured  by  the  tariff, 
and  of  course  opposed  it.  The  growing  sectionalism  between  the  North  and  South 
resulted  in  the  Civil  War. 

Other  vegetable  fibers.  Of  the  several  plants  besides  cotton 
which  are  grown  for  fiber,  only  hemp  and  flax  are  cultivated  to  any 
large  extent  in  the  United  States.     Indeed,  the  latter  is  cultivated 


VEGETABLES  AND   FRUITS 


365 


here  almost  entirely  for  its  seed,  from  which  linseed  oil  is  obtained. 
In  Russia  and  some  other  places,  flax  is  produced  chiefly  for  the  inner 
bark  fiber,  from  which  linen  cloths  are  made.  The  fiber  of  hemp  is  used 
to  make  twine,  rope,  bagging,  etc.  Although  both  plants  can  be  grown 
under  rather  a  wide  range  of  conditions,  the  cultivation  of  hemp  m 
this  country  is  confined  largely  to  Kentucky,  and  that  of  flax  chiefly 
to  the  Dakotas,  Min- 
nesota, and  Montana. 

Tobacco.  The 
United  States  produces 
about  y^  of  the  tobacco 
of  the  world,  its  crop 


UNITED  STATES 

74O,356THOUSAN0 

POUNDS 


in  191 1  being  about 
800,000,000  pounds. 
It  is  grown  in  most 
states  east  of  the  97th 
meridian,  but  a  few 
produce  the  bulk  of  the 
crop  (Fig.  265).  The 
quality  of  the  product 
varies  greatly  with  the 
conditions  of  soil  and 
climate,  and  with  the 
care  used  in  selecting 
the  seed,  cultivating 
the  plants,  and  curing 
the  leaves.  Many 
grades  are  produced. 

Vegetables  and  fruits.  The  growing  of  vegetables  and  fruits 
for  distant  markets  and  for  food  throughout  the  year  has  become  an 
important  industry  mainly  as  a  result  of  (i)  improved  transportation 
facilities,  especially  refrigerator  cars,  and  (2)  the  development  of  the 
canning  industry  (pp.  379,  386).  It  is  impracticable  to  consider  here 
the  many  fruits  and  vegetables  now  grown  for  commercial  purposes 
in  the  United  States.  Some  have  been  mentioned  (pp.  119,  297, 298). 
Potatoes  rank  first  in  value  among  vegetables,  and  apples  among 
fruits;  the  cultivation  of  both  is  distributed  widely. 

The  influence  of  refrigerator  cars  on  the  rise  of  industries  involving  the  ship- 
ment of  perishable  foodstuffs  has  been  very  great.  The  fruit  and  vegetable  indus- 
tries of  the  South  and  the  deciduous  fruit  industry  of  the  far  West  owe  their 


Fig.  265.  Average  annual  production  of  tobacco 
in  different  states  (i 900-1  qo8).  Figures  represent 
production  in  thousands  of  pounds.  (After  Mid- 
dleton  Smith.) 


366  DISTRIBUTION  OF  INDUSTRIES 

development  largely  to  the  refrigerator  car.  It  has  enabled  California,  though 
one  of  the  states  farthest  from  the  chief  city  markets,  to  become  the  leading  fruit- 
growing state  (p.  297). 

In  many  places,  the  refrigerator  car  helped  change  various  fruits  and  vegetables 
from  luxuries,  obtainable  during  a  short  season  only,  to  staple  articles  of  food 
available  during  a  long  season,  or  throughout  the  year.  For  example.  New  York 
City  formerly  obtained  cantaloups  during  a  few  weeks  only  from  New  Jersey, 
Delaware,  and  Maryland.  Now  the  season  for  them  in  New  York  lasts  from  early 
May  to  late  October,  and  some  of  them  come  from  the  Pacific  coast. 

Sugar  plants.  Sugar-cane  is  a  tropical  and  sub-tropical  plant, 
and  its  cultivation  in  the  United  States  is  confined  to  the  Gulf  States, 
Georgia,  and  South  Carolina.  Louisiana  grows  more  than  9/io  of 
the  total  crop  of  the  country.  In  191 1,  690,000,000  pounds  of  cane- 
sugar  were  produced  in  the  United  States. 

The  sugar-beet  was  brought  to  this  country  some  forty  years 
ago  from  central  Europe,  and  in  recent  years  its  cultivation  has 
spread  rapidly.  California,  Michigan,  Colorado,  Utah,  Idaho,  and 
Wisconsin  lead  in  the  production  of  sugar-beets,  but  the  industry 
has  some  importance  in  a  dozen  other  states.  In  the  West,  sugar- 
beets  are  grown  largely  on  irrigated  lands.  The  production  of 
beet-sugar  in  the  United  States  increased  about  sixfold  between 
1900  and  191 1,  amounting,  in  the  latter  year,  to  more  than 
a  billion  pounds. 

Animal  Products  of  Farm  and  Range 
Cattle.  Cattle  are  raised  in  the  United  States  chiefly  for  beef, 
dairy  products,  and  hides.  Fig.  266  shows  that  most  of  the  milch 
cows  are  in  the  more  densely  settled  eastern  half  of  the  country,  and 
that  in  the  eastern  half,  most  are  in  the  northern  states.  The  many 
cities  and  villages  of  the  North  Atlantic  and  North  Central  States 
require  an  enormous  quantity  of  milk,  and  cannot  draw  their  daily 
supplies  from  great  distances.  Herds  may  be  kept  at  a  greater 
distance  from  market  in  connection  with  the  manufacture  of  butter, 
cheese,  and  condensed  milk  (p.  386). 

Fig.  267  indicates  the  distribution  of  cattle  other  than  milch 
cows.  This  map  differs  from  the  preceding  one  in  the  smaller 
numbers  for  the  North  Atlantic  States  and  the  greatly  increased 
numbers  in  the  Great  Plains  and  western  states.  Large  parts  of 
the  Great  Plains  afford  the  best  en\dronment  for  cattle  in  the 
country,  and  much  of  the  land,  furthermore,  cannot  be  used  for 
growing  crops  (p.  329).     Extensive  areas  are  required  for  grazing 


THE  CATTLE  INDUSTRY 


367 


large  herds  of  cattle,  and  with  the  growth  of  population  in  the 
East  much  land  so  used  in  earlier  years  has  been  devoted  to  other 
Durposes.     The  United  States  has  about  V?  of  the  world's  cattle. 


UNITLD  STATES 
17.987  THOUSAND 
MILCH  COWS 


Fig.  266.     Milch  cows  on  farms  and  ranges.     Average  annual  number  in 
thousands  (1899-1908).     (After  Middleton  Smith.) 


UNITED  STATES 
42.650.TH0USAND 
CATTLE. 


Fig.  267.     Cattle   other  than  milch  cows   on   farms  and   ranges.     Average 
annual  number  in  thousands  (1899-1908).     (After  Middleton  Smith.) 


368 


DISTRIBUTION  OF  INDUSTRIES 


Sheep,  Sheep  are  raised  for  mutton  and  wool.  During  the 
last  fifty  years  a  great  change  has  occurred  in  their  distribution. 
The  number  in  most  of  the  middle  and  eastern  states  has  decreased, 
while  in  the  western  states  it  has  increased  greatly.  At  the  beginning 
of  the  period,  the  West  had  less  than  Vio  of  the  sheep  of  the  country; 
now  it  has  more  than  /^  (Fig.  268;  What  are  the  probable  reasons 
for  the  change?).     The  annual  wool  clip  of  the  United  States  is  more 


UNITED  5TATES 

52.206  TMOUSAND 

iHEEP. 


Fig.  268.     Sheep  on  farms  and  ranges. 
(1899-1908).     (After  Middleton  Smith.) 


Average  annual  number  in  thousands 


than  300,000,000  pounds;  nearly  all  of  it  is  used  in  American  fac- 
tories, and  in  addition  much  is  imported. 

Swine.  About  Vs  of  the  swine  of  the  world  are  in  the  United 
States.  While  they  are  raised  more  or  less  in  every  state,  the  great 
swine  region  (Fig.  269)  is  the  same  as  the  leading  corn-producing 
section  (Fig.  259),  for  corn  is  the  chief  food  for  swine.  Nearly  half 
the  corn  crop  is  disposed  of  in  this  way. 

Horses.  A  comparison  of  Fig.  270,  showing  the  distribution  of 
horses  in  the  United  States,  with  Fig.  257,  showing  the  improved 
acreage  and  its  relation  to  the  total  farm  area  in  the  different  states, 
indicates  that  the  number  of  horses  in  the  different  states  corresponds 
roughly  to  the  amount  of  land  cultivated.  This  is  less  striking  in 
some  of  the  southeastern  states,  where  many  mules  are  used  to  cul- 


SHEEP,  SWINE,  AND  HORSES 


369 


tivate  the  land,  because  they  can  stand  hard  work  in  that  climate 
better  than  horses. 

The  total  value  of  farm  animals  in  the  United  States  in  1910  was 
about  $5,000,000,000. 


£        •      /  ) 
r         •       < 

\      J  '"       / 

^^97       \              / 

S3 
7                    • 

)7            ] 

1               • 

tr 

,320  V^^T//                               \ 

\        1  UNITED  STATES 
V,   /  48.565  THOUSAND 
^^             SWINE. 

179              1 

1      • 

MO 

^^ 

\ 

..,.,    I  ^^B 

2r07^^ 

A 

•^ 

I     24 

\ 

,  1216 

2620 

• 

^ 

1177             ^     12 
J-y,            (l334 

rHBB 

Fig.  269.     Swine  on  farms  and  ranges.     Average  annual  number  in  thousands 
(1899-1908).     (After  Middleton  Smith.) 


UNITED  STATtS 

I«t929TH0U5AND 

HORSES. 


Fig.  270.    Horses  on  farms  and  ranges.     Average  annual  niunber  in  thousands 
(1899-1908).     (After  Middleton  Smith.) 


37° 


DISTRIBUTION  OF  INDUSTRIES 


Poultry  and  eggs.  Poultry  and  eggs  are  incidental  products 
of  most  farms.  In  recent  years  poultry-raising  has  become  also 
a  specialized  industry  of  importance,  particularly  in  the  leading 
corn-producing  states  and  near  some  of  the  larger  cities.  The  value 
of  the  poultry  and  eggs  produced  yearly  in  the  United  States  is  nearly 
$300,000,000. 

Forest  Resources  and  Lumbering 

The  forests  of  the  United  States  have  been  a  chief  factor  in  the 
progress  of  the  country.  They  have  furnished  firewood  and  materials 
for  buildings,  furniture,  implements,  utensils,  vehicles,  fences,  paper, 


rOREST   REGIONS 

OFTHE 
UNITED   STATES 

The  Unshaded  Areas  a»-eTreeTes» 
Dtcepf  Aior>5  the  Streams 


Fig.  271.  Map  showing  forest  regions  of  the  United  States.  Not  all  the  land 
within  the  shaded  areas  had  forests,  and  much  has  been  cleared.  The  unshaded 
areas  have  few  forest  trees.     (U.  S.  Forest  Service.) 

posts,  poles,  cross-ties,  ships,  railroad  cars,  bridges,  sidewalks,  etc. 
Our  dependence  on  the  forests  for  material  for  many  things  is  less 
than  formerly.  Thus,  coal  is  now  used  extensively  as  fuel;  brick, 
stone,  and  cement  for  buildings;  iron  and  steel  for  ships,  freight 
cars,  bridges,  etc. ;  wire  for  fences;  and  cement  for  sidewalks.  Never- 
theless, the  yearly  drain  upon  the  forests  has  increased  rapidly. 
The  United  States  is  the  leading  wood-producing  country,  and  it  is 
estimated  that  its  total  annual  consumption  (including  that  de- 


FOREST  RESOURCES  AND  LUMBERING 


371 


stroyed  by  forest  fires)  may  amount  to  100,000,000,000  or  more  board- 
feet.^    The  total  value  of  the  forest  products  in  1909  is  estimated  at 

about    $1,250,000,000.      

Forest  regions  of 
the  United  States. 
Forests  still  cover 
about  yi  the  area  of 
the  United  States. 
Although  the  present 
forest  land  is  more  than 
Vs  the  original  area,  the 
amount  of  good  timber 
remaining  probably  is 
not  more  than  half  the 
original  amount.  This 
is  very  significant  in 
view  of  the  compara- 
tively short  time  the 
forests  of  the  country 
have  been  supplying 
timber.  Fig.  271  shows 
the  five  great  forest 
regions  of  the  country. 

(i)  The  Northern  For- 
est contains  both  soft  and 
hard  woods,  though  the  for- 
mer have  been  most  impor- 
tant. The  leading  kinds 
of  trees  include  white  pine, 
red  pine,  spruce,  hemlock, 
cedar,  balsam- fir,  birch, 
cherry,  and  sugar  maple. 
(2)  The  Hardwood  Forest 
contains  oak,  elm,  hickory, 
Cottonwood,  maple,  bass- 
wood,  chestnut,  ash,  etc., 
not  all  of  which  are  hard. 

Cottonwood  and  basswood,  for  example,  are  soft.  (3)  In  the  Southern  Forest  the 
yellow  pine  predominates,  but  in  places  suited  to  their  growth  are  cypress,  oak, 
gum,  magnolia,  and  other  hardwoods.  (4)  The  Rocky  Mountain  Forest  is  almost 
entirely  coniferous;  leading  trees  are  the  western  yellow  pine,  lodge-pole  pine, 
Douglas  fir,  larch,  spruce,  and  western  red  cedar.     (5)  The  Pacific  Forest  is  also 

^  A  board-foot  is  a  piece  of  wood  one  foot  square  and  one  inch  thick. 


Billions  of  Feet 

1234 

s 

Yellow  Pine  1 

Dong.  Fir... 

Oak 

White  Pine.. 

Hemlock 

Suruce 

Western  Pine 

Maple 

Cypress 

■iW 

^= 

^^^ 

^l' 

■ 

■■■■■ 

^^1 

^^^^^ 

^^^" 

^^™ 

^^^ 

^^^ 

^^™ 

^^^" 

^^^ 

1 

^^^^^ 

^^^^H 

^^^1 

■ 

^^H 

Yel  Poplar. . 

I^^H 

Red  Gum . . . 

^■B 

Chestnut 

^■i 

Redwood. . . . 

■■ 

Beech  

^B 

Birch 

^B 

Basswood . . . 

Elm 

Cedar 

Hickory 

ish 

Cottonwood. . 

Larch  

Tamarack . . . 

Balsam  Fir. . 

Su^.  Pine... 

Tupelo 

White  Fir . . . 

Sycamore .  . . 

Walnut 

Cherry 

1 

Lodgep'l  Pine 

1 

All  others... 

1 

Fig.  272.    Diagram  showing  lumber  cut  for  1909, 
by  kinds  of  wood.     (U.  S.  Forest  Service.) 


372 


DISTRIBUTION  OF  INDUSTRIES 


coniferous,  consisting  chiefly  of  Douglas  fir,  western  yellow  pine,  redwood,  western 
red  cedar,  sugar  pine,  etc.     Fig.  272  shows  the  lumber  production   for   1909, 

by  kinds  of  wood.  The  cut  of 
yellow  pine  equaled  that  of 
the  four  next  most  important 
kinds;  white  pine,  long  in 
the  lead,  ranked  fourth.  Thes-^ 
facts  reflect  the  recent  rapid 
growth  of  lumbering  in  the 
southern  and  western  states, 
and  its  gradual  decUne  in  the 
Lake  states. 

Distribution  of  the 
lumbering  industry.  As 
would  be  expected  from  the 
distribution  of  the  forests, 
lumbering  is  carried  on  in 
every  state,  but,  as  Fig. 
273  shows,  the  production 
varies  greatly.  For  many 
years  the  northeastern 
states,  especially  Maine 
and  New  York,  led  in  lum- 
bering. Since  1850,  the  in- 
dustry has  declined  greatly 
in  that  region.  The  forests 
of  the  Great  Lakes  region 
were  the  next  to  be  used 
extensively    (p.   283),   fur- 


nishing in  1880  about 
the  lumber  cut  of  the 
country.  Michigan  and 
Wisconsin  became,  each  in 
turn,  the  leading  lumbering 
state;  now  they  rank  tenth 
and  eighth,  respectively 
(Fig.  273).  At  present,  the 
southern  states  contribute 
most  to  the  lumber  output 
(Fig.  273);  but  the  indus- 
try is  expected  to  reach  its 
climax  there  within  a  few 


— 

ik 

Billions  of  Feet 
1234 

Wash..l 

T   n 

^^" 

La   .    . 
Miss.. . 
N.C. 
Ark,,. 
Va.... 
Tex... 
Wis.., 
Ore..,. 
Mich, . 
Ala.  .. 

1 

^^ 

^^^^ 

■ 

^^^™ 

■ 

1 

1 

1 

^^^5 

^^^5 

^^^™ 

^^^H 

^^^™ 

^^^^^ 

^^^B 

Minn.. 
Penn. . 
VV.  Va. 
Ga,.,, 
Tenn. . 

I'ld 

Cal,,,, 
Me..,, 

IHH 

H^B 

^^H 

^^ 

■ 

g 

I 

1 

S,  C„, 

■■■■ 

Ky.... 

^^^B 

N.Y,.. 

^^IB 

Mo.... 

l^i^ 

N.H.. 

^■a 

Ida.... 

^IHI 

Ind.... 

^am 

Ohio... 

■■■ 

Mass.. 

■i 

Vt 

■i 

Mont. . 

^ 

Md.... 

■ 

Okla... 

■ 

m 

■ 

Conn.. 

■ 

Col.... 

■ 

Iowa . . 

■ 

N,  M.. 

■ 

Ariz, . , 

N.J,.. 

Del..,. 

S  D... 

Wyo... 

R,  1... 

1 

Utah. 

1 

Kas   . 

■1 

: ^1 

Fig.  273,    Diagram  showing  lumber  produc- 
tion by  states  in  1909,    (U,  S.  Forest  Service.) 


CONSERVATION  OF  FOREST  RESOURCES  373 

years,  and  already  the  Pacific  states  are  large  producers.  Indeed. 
Washington  is  now  the  leader. 

Conservation  of  forest  resources.  About  260  cubic  feet  of 
wood  per  capita  per  year  are  consumed  in  the  United  States.  This 
is  greater  than  the  rate  of  consumption  in  any  other  country,  about 
ten  times  that  in  France,  and  seven  times  that  in  Germany.  Stated 
in  another  way,  w^e  are  taking,  on  the  average,  40  cubic  feet  of  wood 
per  acre  per  year  from  our  forests.  Since  the  average  growth  in  the 
forests  of  the  United  States  is  not  at  present  more  than  12  cubic  feet 
per  acre  per  year,  we  are  consuming  wood  more  than  three  times  as 
fast  as  it  is  grown  in  our  forests.  The  United  States  cannot  in  the 
long  future  count  on  foreign  sources  of  supply  for  ordinary  structural 
timber,  for  other  countries  probably  will  need  all  they  can  grow. 
Therefore,  if  there  is  to  be  a  permanent  supply  of  wood  in  this 
country,  we  cannot  long  continue  to  use  more  than  our  forests 
produce.  Clearly,  every  means  of  reducing  the  drain  upon  the 
forests,  and  every  means  of  increasing  their  production,  should  be 
encouraged. 

Altogether  apart  from  a  supply  of  timber,  the  preservation  of 
forests  in  many  places  is  desirable  (i)  to  reduce  soil  erosion  and  the 
resultant  deposition  of  waste  on  lower  lands,  in  stream  channels,  and 
in  harbors  (p.  167) ;  (2)  to  make  floods  less  frequent  and  less  dangerous 
(p.  237);  and  (3)  to  help  equalize  the  flow  of  streams  important  for 
navigation,  power  (p.  290),  or  irrigation  (p.  298). 

The  principal  ways  in  which  the  forest  resources  of  the  United  States  should 
be  conserved  may  be  indicated  briefly,  (i)  Losses  from  fires  should  be  reduced 
(Fig.  274).  The  average  annual  loss  of  merchantable  timber  is  estimated  at  about 
$50,000,000.  In  addition,  many  lives  have  been  lost  in  some  forest  fires,  and 
villages  have  been  consumed,  (b)  Great  loss  is  involved  in  the  damage  to  young 
trees  and  seedlings,  (c)  After  high-class  timber  is  burned  off  an  area,  the  latter 
may  be  occupied  by  inferior  kinds  of  timber,  (d)  The  humus  in  the  soil  may  be 
consumed,  reducing  or  destroying  the  fertility  of  the  latter,  (e)  Erosion  may 
increase  on  burned-over  areas,  and  the  flow  of  streams  may  become  more  uneven. 
Forest  fires  are  started  by  sparks  from  locomotives,  by  careless  campers  and 
hunters,  by  careless  clearing  and  brush  burning,  by  lightning,  and  in  other  ways. 
Save  those  due  to  lightning,  nearly  all  may  be  prevented.  So  far  as  its  funds 
permit,  the  Forest  Service  maintains  a  patrol  in  the  National  Forests,  partly  with 
a  view  to  detecting  fires  at  their  beginning,  and  fighting  them  while  they  are 
still  small.  Some  state  and  private  forests  also  are  patrolled  during  the  dry 
season. 

(2)  Waste  in  logging  should  be  reduced  so  far  as  practicable.  At  present  it 
averages  about  25%  in  the  timber  holdings  of  individuals  and  companies,  and 
something  less  than  10%  in  the  National  Forests.     In  connection  with  logging 


374 


DISTRIBUTION  OF  INDUSTRIES 


operations,  young  trees  should  be  protected,  and  seed  trees  should  be  left.  (3) 
The  wastes  in  sawmills  and  wood-using  industries  should  be  reduced.  (4)  Refuse 
wood  may  be  used  in  making  many  things  now  manufactured  from  good  timber. 
(5)  Wherever  practicable,  forest  areas  should  be  kept  fully  stocked  with  rapid- 
growing  and  valuable  species  of  trees.  In  this  way  the  production  of  wood  in 
existing  forests  may  be  increased  greatly.  (6)  In  many  places,  cut-over  or  burnt- 
over  areas  should  be  reforested.      (7)  Posts,  poles,  cross-ties,  mine  timbers,  pilings, 


Fig.  274.  Effects  of  hurricane  and  fire  in  a  heavy  stand  of  white  pine  on  the 
Little  Fork  of  St.  Joe  River,  Coeur  d'Alene  National  Forest,  Idaho.  (U.  S.  Forest 
Service.) 

shingles,  etc.,  may  be  treated  with  some  preservative  substance,  such  as  creosote, 
and  thus  rendered  less  subject  to  decay  and  to  the  attack  of  insects.  Wood  treated 
in  this  way  lasts  10  to  18  or  more  years  longer  than  wood  not  so  treated.^  The 
general  adoption  of  the  practice  of  treating  with  preservatives  wood  used  in  the 
above  ways  would  not  only  lessen  the  drain  on  the  forests,  but  also  give  value  to 
much  inferior  timber.  (8)  The  enormous  waste  of  forest  resources  caused  by  in- 
sects can  be  reduced  greatly.  (9)  The  wasteful  methods  generally  followed  in 
the  turpentine  industry  (p.  380)  should  be  abandoned.  (10)  For  many  purposes, 
other  material  may  be  substituted  advantageously  for  wood  (p.  176).  (n)  Recently 
much  has  been  done  to  conquer  the  diseases  of  forest  trees,  and  much  more  may 
be  done  in  the  future.     (12)  Standing  timber  is  taxed  in  most  states  each  year, 


NEW  ENGLAND   FISHERIES  375 

and  this  leads  owners  in  many  cases  to  cut  all  their  timber  and  put  it  on  the 
market  as  soon  as  possible.  Before  the  principles  of  scientific  forestry  can  be 
adopted  generally,  these  tax  laws  must  be  reformed. 


The  Fishing  Industries 

Nature  and  general  distribution.  Fishing  on  a  commercial 
scale  is  carried  on  from  many  places  on  the  coasts  of  the  United 
States,  and  on  many  inland  streams  and  lakes.  The  total  annual 
value  of  the  products  of  the  fisheries  has  exceeded  $60,000,000  in 
recent  years,  the  products  of  the  coast  and  ocean  fisheries  making 
nearly  ^  of  the  total.  The  products  include  not  only  food-fishes, 
but  the  commercial  products  derived  from  all  other  marine  and 
fresh-water  animals.  About  Vs  of  the  products  are  furnished  by 
animals  other  than  fishes,  such  as  clams,  oysters,  lobsters,  shrimps, 
sponges,  whales,  and  fur-seals.  The  leading  fish  of  commercial  im- 
portance are  salmon,  cod,  shad,  menhaden,  mackerel,  squeteague  (or 
sea  trout),  haddock,  herring,  and  trout. 

Most  marine  fishing  industries  are  favored  by  (i)  extensive  areas 
of  shallow  water  off  shore,  to  serve  as  feeding  and  breeding  grounds 
for  large  numbers  of  fish;  (2)  convenient  harbors  affording  safe  havens 
for  fishing  boats;  and,  where  the  industry  is  dependent  on  the  sale  of 
fresh  fish,  (3)  nearness  to  large  centers  of  population.  With  present 
facilities  for  transportation  and  refrigeration,  the  last  point  is  less 
important  than  formerly. 

Where  poor  soil,  rugged  surface,  or  rigorous  climate  has  made  farming  in 
coastal  regions  unprofitable,  the  people  have  turned  to  the  ocean  for  a  living.  They 
become  fishermen,  develop  into  expert  sailors  and  navigators,  and  supply  men  for 
the  great  merchant  fleets  of  the  world. 

Atlantic  coast  fisheries.  Since  early  colonial  days,  the  fishing 
industries  of  the  Atlantic  coast  have  centered  in  New  England, 
which  had  all  the  advantages  mentioned  above.  Cod,  haddock, 
mackerel,  and  herring  are  taken  in  largest  quantities. 

Most  of  the  early  settlements  along  the  eastern  coast  of  New  England  had 
fishing  fleets,  and  many  of  them  depended  almost  entirely  on  the  industry.  For 
many  years,  cod  was  the  leading  export  of  New  England.  The  better  fish  were 
taken  to  southern  Europe,  while  those  of  poorer  quality  were  sold  in  great  quanti- 
ties in  the  West  Indies  to  feed  the  slaves.  Here  salted  cod  was  cheaper  and  more 
wholesome  than  meat,  and  would  keep  much  longer.  In  early  days  many  fishing 
towns  were  scattered  along  the  New  England  coast  at  points  where  the  advantages 
of  harbors  and  nearness  to  good  fishing  grounds  were  combined,  and  the  industry 


376  DISTRIBUTION  OF  INDUSTRIES 

was  carried  on  chiefly  from  small  boats  near  land.  As  the  supply  of  fish  near  at 
hand  was  reduced,  larger  vessels  were  built  for  use  on  the  distant  banks,  and  the 
industry  centered  in  a  few  places  having  special  advantages.  Gloucester  has  the 
best  harbor  on  Cape  Ann,  and  was  the  first  fishing  port  of  the  district  to  seciure  rail- 
road connection  with  Boston.  Accordingly,  the  industry  developed  rapidly  there, 
while  it  declined  at  less  favored  neighboring  towns.  To-day,  Gloucester  and  Bos- 
ton are  the  most  important  fishing  ports  in  the  United  States. 

The  whaling  industry  was  important  in  New  England  for  many  years,  although 
insignificant  now.  Several  things  caused  its  rapid  decline  during  the  third  quarter 
of  the  last  century,  especially  (i)  the  growing  scarcity  of  whales  and  (2)  the  dis- 
covery of  petroleum  in  Pennsylvania. 

The  oyster  is  the  most  important  shell-fish.  It  thrives  best 
in  relatively  warm  waters,  and  in  quiet,  shallow  estuaries  and  bays, 
such  as  those  between  Long  Island  Sound  and  Chesapeake  Bay. 
Some  Vs  of  the  oysters  marketed  in  the  United  States  come  from  this 
part  of  the  coast.  At  first  the  industry  depended  entirely  on  natural 
beds  of  oysters;  but  as  the  natural  supply  declined,  the  practice  grew 
up  of  "planting"  young  oysters,  and  leaving  them  to  mature. 

Pacific  coast  fisheries.  The  salmon  fisheries  are  the  most 
important  ones  on  the  Pacific  coast,  but  cod  and  halibut  are  caught 
in  large  numbers.  The  salmon  industry  is  centered  in  Alaska, 
about  the  shores  of  Puget  Sound,  and  on  the  Columbia  River.  Most 
of  the  fish  are  caught  in  traps  and  weirs  during  the  spring  or  summer 
run,  when  they  ascend  the  rivers  to  spawn.  At  such  times,  the 
waters  sometimes  have  been  so  congested  with  salmon  that  the  near- 
by canneries,  working  night  and  day,  have  found  it  difficult  to  handle 
the  fish  brought  in.  Canned  salmon  is  the  largest  fish  export  of  the 
United  States. 

In  Alaska,  the  salmon  fisheries  rank  next  to  gold  mining  in  value  of  output. 
The  total  value  of  their  product  since  1868  is  said  to  be  more  than  $130,000,000,  or 
more  than  eighteen  times  the  amount  the  United  States  paid  for  Alaska  in  1867. 

The  largest  fur-seal  herd  in  the  world  uses  the  cool,  moist  Pribilof 
Islands  (Bering  Sea)  as  a  breeding  ground,  but  the  estimated  number 
of  animals  in  it  was  reduced  from  some  5,000,000  in  1867  to  about 
200,000  in  1905.  In  recent  years  steps  have  been  taken  to  prevent 
the  extermination  of  the  herd,  and  to  put  the  fur-sealing  industry  on 
a  permanent  basis. 

Mining,  Quarrying,  etc. 

The  principal  mineral  resources  of  the  United  States,  together  with 
their  uses  and  economic  significance,  were  noted  in  Chapter  XIII. 
The  mining  and  quarrying  of  these  resources  afford  employment  to 


FACTORS  AFFECTING  MINING  377 

hundreds  of  thousands  of  people,  and  furnish  raw  material  or  fuel  for 
many  other  industries.  The  total  value  of  the  mineral  products  of 
the  United  States  in  1910  v/as  about  $2,003,000,000.  The  accom- 
panying table  shows  the  production  of  the  leading  mineral  substances 
in  that  year. 

Quantity  Value 

Pig  Iron 27,303,567  long  tons         $425,115,235 

Copper 1,080,159,509  pounds  137,180,257 

Gold 4,657,018  troy  ounces        96,269,100 

Lead 372,227  short  tons  32,755,976 

Silver 51,137,900  troy  ounces         30,854,500 

Zinc 252,479  short  tons  27,267,732 

Aluminum 47,734,000  pounds  8,955,700 

Bituminous  coal 417,111,142  short  tons         469,281,719 

Pennsylvania  anthracite 75)433)246  long  tons  160,275,302 

Natural  gas 70,756,158- 

Petroleum 209,556,048  barrels  127,896,328 

Clay  products 170,115,974 

Cement 77,785,141  barrels  68,752,092 

Stone 76,520,584 

Other  structural  materials   40.821,793 

Gypsum 2,379,057  short  tons  6,523,029 

Phosphate  rock 2,654,988  long  tons  10,917,000 

Salt 30,305,656  barrels  7,900,344 

Mineral  waters 62,030,125  gallons  6,357,590 

Distribution  of  mineral  industries.  In  general,  the  distribu- 
tion of  mineral  deposits  (pp.  175-183)  controls  that  of  mining  and 
quarrying,  but  whether  or  not  a  given  mineral  deposit  can  be  worked 
profitably  depends  on  several  things.  Chief  among  these  are  (i) 
its  size,  (2)  its  quality,  (3)  its  location,  (4)  the  cost  of  working  it, 
and  (5)  market  conditions.  The  relative  importance  of  these  fac- 
tors varies  greatly  with  different  minerals. 

(i )  In  many  places  minerals  of  value  occur  in  quantities  too  small 
to  mine.  The  opening  and  equipment  of  a  modern  mine  might  be 
justified  by  a  small  deposit  of  a  valuable  mineral,  like  gold  or  silver, 
but  might  not  be  warranted  by  a  vastly  larger  deposit  of  a  cheap  min- 
eral, like  iron.  (2)  There  is  much  low-grade  ore  and  coal  that  cannot 
be  mined  profitably  in  competition  with  better  material  of  the  same 
kind.  For  example,  the  United  States  is  estimated  to  have  more  than 
75  billion  long  tons  of  low-grade  iron  ore,  not  available  (i.  e.,  not 
workable  with  profit)  under  existing  conditions,  as  against  less  than 
5  billion  tons  which  are  available.     (3)  The  importance  of  location 


378  DISTRIBUTION  OF  INDUSTRIES 

is  greatest  in  the  case  of  minerals  which  are  abundant  and  cheap,  and 
least  in  the  case  of  those  of  great  value.  Thus  iron  ore  which  could 
be  mined  with  a  small  profit  if  near  the  shores  of  the  Great  Lakes, 
probably  could  not  be  mined  if  in  Utah.  On  the  other  hand,  gold  offers 
great  value  in  small  bulk,  and  so  can  be  transported  easily.  In 
recent  years,  therefore,  it  has  attracted  thousands  of  men  to  remote 
sections  of  Alaska,  where  most  other  minerals  could  not  be  mined 
with  profit.  The  discovery  of  gold  in  California  in  1848  brought 
nearly  50,000  miners  there  in  1849,  added  a  new  state  to  the  Union 
in  1850,  and  gave  it  a  population  of  360,000  in  i860.  (4)  Relatively 
cheap  minerals  are  mined  only  where  they  occur  in  favorable  posi- 
tions, rather  near  the  surface;  those  of  greater  value  justify  deeper 
mines  and  greater  expense.  In  classif>dng  coal  lands,  the  United 
States  Geological  Survey  has  taken  a  depth  of  3,000  feet  as  the  present 
limit  for  coal  mining.  Some  of  the  copper  mines  of  the  Lake  Superior 
region  are  more  than  a  mile  deep.  (5)  The  output  of  many  mines  and 
quarries  is  affected  greatly  by  the  demand  for  the  product.  The  total 
value  of  the  mineral  products  of  the  country  declined  from  $2,071,- 
000,000  in  1907  to  $1,595,000,000  in  1908,  largely  as  a  result  of  the 
business  depression  which  began  late  in  1907. 

The  influence  of  mining  on  the  distribution  of  population  and 
the  growth  of  cities  is  discussed  elsewhere  (pp.  315,  330,  397,  403). 

Manufacturing  Industries 

Growth  of  manufacturing  industries.  For  many  years,  most 
manufacturing  in  the  United  States  was  done  in  homes.  The  cloth- 
ing, utensils,  and  implements  used  by  the  people  were  largely  "home- 
made," as  is  still  the  case  in  certain  regions  (p.  309).  There  were 
some  factories  even  in  the  colonial  period,  and  manufactured  goods 
were  imported  from  other  countries,  especially  for  the  wealthier  people. 
By  1820  or  1825,  the  factory  system  was  established  throughout  much 
of  the  country  then  settled.  Since  1850,  and  especially  since  1880, 
the  manufacturing  industries  of  the  United  States  have  grown  with 
great  and  increasing  rapidity  (Fig.  275),  until  now  it  ranks  first  among 
manufacturing  countries.  The  total  value  of  manufactured  products 
for  the  country  amounted, in  i9io,to  more  than $20,000,000,000.  The 
industrial  growth  of  the  last  half -century  has  been  due  to  (i)  the  in 
crease  of  population;  (2)  the  improved  financial  condition  and  higher 
standard  of  living  of  the  people;  (3)  the  increasing  supplies  of  raw 


INDUSTRIES  LOCATED   BY  RAW   MATERIALS     379 

materials;  (4)  the  improvement  of  transportation  facilities;  and  (5) 
the  growing  demand  abroad  for  American  goods. 

The  Location  of  Industries 
Many  manufacturing  centers  specialize  in  a  few  products.  Thus 
Brockton,  Massachusetts,  is  the  leading  boot  and  shoe  center;  Grand 
Rapids,  Michigan,  is  famous  for  its  furniture;  and  Peoria,  Illinois, 
leads  in  distilling  Uquors.  In  some  cases,  as  in  those  cited,  the 
reasons  for  the  development  of  special  industries  in  certain  places 
are  clear;  in  others,  the  causes  are  obscure.     In  general,  the  most 


liillions   of  Doliars 

1       2      3      4       5      6      7       8      9      10    11     12    13    14     15     16    17    18    19    20 

1850 

3- 

1860 

1870 

■^■^P^ 

\  \  \  r 

1880 

1  1  1  1  1 

Fig.  275.  Diagram  showing  total  value  of  manufactured  products  in  the 
United  States  for  the  census  years  1850-1910. 

important  factors  influencing  the  location  of  manufacturing  indus- 
tries are  (i)  distribution  of  raw  material,  (2)  command  of  power, 
(3)  accessibility  of  market,  and  (4)  a  supply  of  labor. 

Distribution  of  raw  material.  The  influence  of  the  distri- 
bution of  raw  materials  in  locating  the  industries  which  use  them  is 
greatest  in  the  case  of  (i)  perishable  raw  materials,  and  (2)  raw 
materials  that  are  too  bulky  and  too  cheap  to  be  carried  far  to  fac- 
tories, (i)  If  prepared  and  handled  carefully,  fresh  fruits  and 
vegetables  may  be  sent  long  distances  in  refrigerator  cars  (p.  365). 
But  it  is  impracticable  to  do  this  with  the  large  quantities  used  in 
the  canning,  preserving,  and  allied  industries.  Hence  these  indus- 
ries  are  located,  for  the  most  part,  near  the  places  of  production. 
Thus,  canning  and  drying  fruit  and  making  wine  are  important  in- 
dustries in  California.  Indeed,  California  furnishes  about  ^/lo  of  the 
dried  fruit  and  some  }i  of  the  wine  made  in  the  United  States.     In 


38o  DISTRIBUTION  OF  INDUSTRIES 

New  Jersey  and  Delaware  ^  of  the  total  canned  product  are  toma- 
toes. Similar  influences  appear  in  the  case  of  many  animal  products. 
The  centering  of  slaughtering  and  meat-packing  in  Chicago,  South 
Omaha,  and  Kansas  City  is  due  partly  to  the  losses  which  result 
from  shipping  live  animals  long  distances.  Butter,  cheese,  and  con- 
densed milk  are  manufactured  extensively  where  large  quantities  of 
milk  are  produced,  as  in  New  York,  Wisconsin,  and  Iowa. 

(2)  Among  the  raw  materials  that  are  too  bulky  or  too  cheap 
to  be  carried  economically  to  distant  points  are  many  of  the  products 
of  the  quarries,  mines,  and  forests.  Hence  the  industries  which  use 
these  materials  are  located  in  most  cases  near  the  sources  of  supply. 
In  some  cases,  on  the  other  hand,  special  conditions  make  it  practi- 
cable to  take  bulky  raw  material  to  remote  manufacturing  plants. 
Thus  granite  from  Massachusetts  or  marble  from  Vermont  is  shipped 
profitably  for  monumental  purposes  throughout  the  country,  because 
■when  cut  and  polished  in  a  local  yard  a  single  piece  may  have  a  market 
value  of  hundreds  of  dollars.  Again,  it  may  be  feasible  to  take  bulky 
raw  material  to  distant  points  because  of  very  cheap  transportation, 
as  in  the  case  of  the  iron  ore  of  the  Lake  Superior  region  (pp.  268,  282). 

The  tendency  of  wood-working  industries  to  keep  close  to  the  lumbering 
■districts  is  indicated  by  the  distribution  of  saw-mills,  wood-pulp  mills,  the  turpen- 
tine industry,  charcoal  burning,  and,  less  strikingly,  furniture  making.  The  wood- 
pulp  industry  was  most  important  originally  in  western  Massachusetts,  and  later 
in  Pennsylvania,  but  as  the  supply  of  pulp-wood  decreased,  the  industry  became 
more  important  elsewhere.  It  is  now  centered  in  Maine,  northeastern  New  York, 
•and  Wisconsin,  where  spruce  and  hemlock,  the  principal  woods  used  in  the  industry, 
are  more  abundant.  These  regions  have  the  additional  advantages  of  abundant 
water  power  and  relatively  near  markets  for  the  finished  products.  The  manufac- 
ture of  furniture  was  carried  on  chiefly  in  the  East  until  some  twenty  years  ago, 
with  New  York  the  leading  center.  Now  Chicago  stands  well  ahead  of  New  York, 
and  Grand  Rapids  is  a  close  third  (p.  288).  This  migration  of  the  industry  fol' 
lowed  the  shifting  of  the  center  of  lumbering  from  the  northeastern  states  to  the 
Great  Lakes  region  (p.  372).  Recently,  the  growth  of  lumbering  in  the  Gulf  states 
and  northwestern  states  (p.  372)  has  led  to  a  rapid  development  of  furniture- 
making  in  those  sections.  The  manufacture  of  tar,  pitch,  and  turpentine  has 
long  been  an  important  industry  in  the  South.  These  things  are  made  chief!}'  from 
the  "sap"  of  the  long-leaf  pine,  and  this  is  obtained,  in  most  cases,  by  frequently 
making  needlessly  large  cuts  in  the  lower  part  of  the  trunk.  The  average  period 
during  which  a  given  tree  furnishes  sap  under  this  method  is  only  four  years,  and 
this  has  caused  a  steady  migration  of  the  center  of  the  turpentine  industry.  North 
Carolina  led  for  a  time,  then  South  Carolina  came  to  the  front.  From  South  Carolina 
the  industry  spread  into  Georgia,  where  it  is  beginning  to  decline.  Now  Florida 
leads,  and  the  industry  is  spreading  rapidly  into  Alabama  and  Mississippi.  The  For- 
■est  Service  has  developed  new  methods  of  obtaining  the  sap  from  smaller  cuts.    The 


INDUSTRIES   LOCATED   BY   POWER  381 

general  adoption  ot  these  methods  will  increase  greatly  the  life  of  the  industry. 
Most  ores,  except  iron,  have  relatively  high  values  for  small  bulk,  but  as  they 
come  from  the  mine,  they  are  likely  to  be  associated  with  much  worthless  material. 
Hence  the  metallic  matter  in  most  cases  is  partly  separated  from  the  waste  (i.e., 
is  concentrated)  at  the  mine.  It  may  also  be  smelted  (metal  extracted  from  the 
ore)  at  the  mine,  but  since  in  its  concentrated  form  it  is  commonly  valuable  enough 
to  bear  rather  heavy  freight  charges,  it  is  shipped  in  many  cases  to  some  big 
smelter,  where  large-scale  operation  reduces  the  cost.  Refining  the  metal  may 
be  done  in  turn  far  from  the  smelter.  Thus,  silver  ore  mined  in  Leadville,  Colo- 
rado, may  be  concentrated  at  or  near  the  mine,  smelted  in  Pueblo,  refined  in 
Jersey  City,  and  manufactured  into  jewelry  in  Providence,  Rhode  Island. 

The  source  of  many  raw  materials  of  high  value  has  little  if  any 

influence  on  the  location  of  the  industries  which  use  them.     This 

is  determined  by  other  factors. 

Many  illustrations  might  be  given.  The  United  States  produces  no  raw  silk 
for  the  many  silk  mills  of  New  York,  New  Jersey,  and  Pennsylvania.  Lowell, 
Massachusetts,  manufactures  large  quantities  of  woolen  goods,  although  New 
England  now  raises  few  sheep  (p.  368). 

Influence  of  power  resources.  Available  power  may  be  the 
leading  factor  determining  the  location  of  manufacturing  plants 
which  use  raw  material  suited  to  economical  transportation.  Water 
power  determined  the  location  of  many  of  the  older  manufacturing 
centers  of  New  England  (p.  288).  Some  of  these  places  had  small 
power  resources,  and  depended  on  the  local  supply  of  raw  material; 
such  places  have  declined.  Others  have  continued  to  grow  because 
they  had  larger  power  resources  and  were  so  situated  that,  as  transpor- 
tation facilities  were  improved,  they  could  use  raw  materials  from 
increasingly  distant  points,  and  could  bring  in  coal  to  supplement 
their  water  power.  There  are  said  to  be  more  than  forty  important 
manufacturing  cities  in  southern  New  England  that  can  trace  their 
start  to  an  early  advantage  in  water  power.  Nearly  all  of  them  now 
use  much  more  steam  power  than  water  power. 

The  use  of  coal  and  steam  power  in  manufacturing  increased 

rapidly  after  1850.     The  growth  of  railroads  steadily  increased  the 

number  of  places  which  could  get  coal,  and  also  made  cheaper  the 

movement  of  raw  materials  to  places  situated  favorably  with  respect 

to  supplies  of  coal.     The  advantage  of  large  deposits  of  good  coal  has 

had  much  to  do  with  the  remarkable  industrial  development  since  1850 

in  the  region  extending  from  western  Pennsylvania  to  Illinois. 

The  use  of  other  mineral  fuels  for  industrial  purposes  also  has  located  certain 
manufactures.  Thus  the  discovery  of  natural  gas  in  western  Pennsylvania,  Ohio, 
Indiana,  and  West  Virginia  attracted  many  industries  because  of  the  cheap  and 


382  DISTRIBUTION  OF  INDUSTRIES 

excellent  fuel  offered.  In  many  places  the  supply  of  natural  gas  failed  after  a 
few  years,  and  as  a  result  many  factories  were  abandoned  or  moved;  some  of  the 
larger  ones  continued  to  operate  by  bringing  in  coal.  California  is  beginning  to 
feel  the  benefit  of  the  large  supplies  of  cheap  oil  discovered  there  within  the  last 
few  years.  Formerly,  the  industrial  development  of  the  state  was  retarded  by  the 
fact  that  much  fuel  had  to  be  imported  at  relatively  heavy  expense. 

As  the  supply  of  fuels  diminishes,  hydro-electric  power  will  be 
used  more  and  more  in  manufacturing  (p.  289).  But  the  ease  of 
transmitting  the  power  to  considerable  distances  removes  the  need 
of  locating  the  factory  near  the  source  of  the  water  power  (p.  288). 

Influence  of  nearness  to  market.  The  advantages  of  a  nearby 
market,  or  of  superior  facilities  for  shipping  goods  to  more  distant 
markets,  have  been  leading  factors  in  determining  the  location  of  many 
industries. 

An  example  is  afforded  by  the  location  of  the  leading  refineries  handling 
imported  cane-sugar.  Sugar  is  refined  and  molasses  is  manufactured  to  some 
extent  in  Louisiana,  where  cane  is  grown.  But  much  cane-sugar  is  imported, 
and  the  largest  refineries  are  in  New  York  and  Philadelphia,  in  part  because 
of  the  heavy  local  consumption  and  the  excellent  means  of  distribution  to  out- 
side markets.  Furthermore,  by  having  the  refineries  at  tidewater  the  cost  of 
transporting  the  raw  material  is  reduced. 

A  more  striking  case  is  that  of  the  manufacture  of  agricultural  implements. 
The  chief  market  for  these  things  is  in  the  leading  farming  sections.  Many  im- 
plements are  very  heavy  and  occupy  much  car-space,  so  that  freight  rates  on  them 
are  high.  For  their  manufacture,  there  is  accordingly  great  advantage  in  a  loca- 
tion near  the  chief  market.  As  a  result,  there  has  been  a  steady  westward  migra- 
tion of  the  industry  as  the  great  grain  districts  have  expanded  in  that  direction 
(p.  361).  In  1880,  Ohio  and  New  York  were  leaders  in  the  industry;  now,  Illinois 
is  far  ahead  of  both  combined,  its  output  having  increased  threefold  between 
1880  and  1910. 

Influence  of  supply  of  labor.  The  importance  of  a  local  sup- 
ply of  labor  in  determining  the  location  of  manufactures  varies  great- 
ly. It  depends  in  part  on  the  character  of  the  industry,  being  more 
important  in  the  case  of  industries  requiring  skilled  labor  than  in 
others.  In  general,  it  is  much  less  important  now  than  formerly, 
for  it  has  become  increasingly  easy  to  attract  laborers  to  any  given 
point  where  other  conditions  are  favorable.  Doubtless,  too,  labor 
will  be  even  more  mobile  in  the  future. 

In  the  past,  manufacturing  in  parts  of  the  South  and  in  California  has  been 
retarded  by  lack  of  a  satisfactory  supply  of  labor.  On  the  other  hand,  the  leader- 
ship of  New  York  City  in  the  ready-made  clothing  industry  is  due  in  part  to  the 
presence  of  abundant  cheap  labor.  The  supremacy  of  New  England  in  the  manu- 
facture of  cotton  has  been  maintained  of  late  years  largely  through  the  possession 
of  expert  workers. 


IMPORTANCE  OF  URBAN  INDUSTRIES  383 

Other  factors.  In  addition  to  the  leading  factors  discussed 
above,  there  are  various  minor  factors  which  may  influence  the 
location  of  manufacturing  industries.  Thus  the  advantage  of  an 
early  start  has  located  certain  industries  in  places  without  superior 
natural  advantages.  In  most  cases  this  advantage  is  associated 
closely  with  the  question  of  labor. 

The  boot  and  shoe  industry  of  Brockton,  Lynn,  and  Haverhill,  Massachusetts, 
illustrates  the  advantage  of  an  early  start.  The  industry  was  established  in  these 
places  at  an  early  date,  and  by  enlisting  the  services  of  many  of  the  people,  a 
supply  of  skilled  labor  was  developed  with  enough  impetus  to  give  first  rank  to 
the  localities.  Most  of  the  shoe  factories  of  these  cities  are  run  by  steam  power, 
developed  from  Pennsylvania  coal,  and  most  of  the  leather  they  use  is  tanned 
in  other  states.  Clearly,  their  leadership  rests  on  an  insecure  basis,  and  the 
business  is  growing  fast  in  other  cities  having  more  fundamental  advantages. 

In  earlier  years,  industries  frequently  were  established  in  particular  places 
because  of  a  supply  of  local  capital,  but  now  such  cases  are  relatively  few  and 
unimportant.  Broadly  speaking,  capital  is  perfectly  mobile,  and  goes  wherever 
other  conditions  are  favorable.  Chmate  may  also  be  a  direct  factor  in  determin- 
ing the  location  of  manufacturing  industries,  though  its  influence  is  offset  easily 
by  other  considerations.  Thus  the  climate  of  the  northern  states  is  more  invigorat- 
ing than  that  of  the  southern  states,  and  workingmen  are  likely  to  render  more 
efficient  service,  on  the  average,  in  the  former  than  in  the  latter.  Yet  because  of 
other  advantages,  the  manufacturing  industries  of  the  South  are  growing  rapidl>. 

Combined  influence  of  various  factors.  While  many  indus- 
tries are  located  largely  or  wholly  by  one  or  two  factors,  the  distri- 
bution of  others  is  the  result  of  the  combined  influence  of  most  o^ 
all  of  the  things  mentioned  above.  Many  industries,  too,  have  been 
located  without  regard  to  the  geographic  and  economic  conditions 
involved,  and  not  a  few  have  failed  for  this  reason. 

Further  illustrations  of  the  leading  factors  which  influence  the 
distribution  of  industries  occur  in  the  following  pages,  in  connection 
with  the  discussion  of  the  leading  manufactures  of  the  country. 

The  leading  manufacturing  states  and  cities.  New  York,  Penn- 
sylvania, Illinois,  Massachusetts,  and  Ohio,  in  this  order,  are  the 
five  leading  manufacturing  states,  while  New  York,  Chicago,  Phila- 
delphia, St.  Louis,  and  Cleveland  are  the  five  most  important  manu- 
facturing cities.  In  1910,  the  combined  value  of  the  manufactured 
products  of  cities  having  a  population  of  10,000  or  more  was  more 
than  twice  that  of  smaller  cities  and  rural  districts.  The  more  rapid 
growth  of  urban  as  compared  with  rural  population  has  been  one  of 
the  most  striking  and  significant  things  in  connection  with  the  popula- 
tion changes  of  recent  years  (p.  399).     It  has  been  due  in  large  part 


384 


DISTRIBUTION  OF  INDUSTRIES 


to  the  rapid  growth  of  urban  industries.  The  factories  in  the  territory 
east  of  the  Mississippi  River  and  north  of  the  Ohio  and  Potomac 
rivers  employ  about  ^  of  all  the  industrial  wage-earners  (not  workers 
on  farms)  of  the  country,  and  contribute  about  the  same  proportion 
of  the  total  value  of  manufactured  products. 

Leading  Manufactures  of  the  United  States 
The  Federal  Census  Bureau  has  divided  the  339  classes  of  manu- 
factures that  are  carried  on  in  the  United  States  into  14  groups. 
These  are  shown  in  the  accompanying  table. 

MANUFACTURING  INDUSTRIES  OF  THE  UNITED  STATES 

[Ranked  according  to  value  of  product  in  igog) 


Group 


Food  and  kindred  products 

Iron  and  steel  and  their 
products 

Textiles 

Lumber  and  its  manu- 
factures   

Chemicals  and  allied  prod- 
ucts   

Metals  and  metal  products, 
other  than  iron  and  steel 

Paper  and  printing 

Vehicles  for  land  transpor- 
tation  

Leather  and  its  finished 
products 

Liquors  and  beverages .... 

Clay,  glass,  and  stone 
products 

Tobacco  manufactures 

Shipbuilding 

Miscellaneous  industries. . . 
United  States 


Year 


1 909 
1899 

1909 
1899 

1909 
1899 
1909 
1899 
1909 
1899 
1909 
1899 
1909 
1899 
1909 
1899 
1909 
1899 
1909 
1899 
1909 
1899 
1909 
1899 
1909 
1899 
1909 
1899 


1909 
1899 


Number  of 
establish- 
ments 


55,364 
41,247 
17,289 
14,080 

21,695 
17,640 

48,533 
34,947 

11,745 
8,687 

8,750 

4,996 

34,828 

26,627 

8,248 
8,738 
5,728 
5,625 

7,347 
5,740 
16,168 
11,524 
15,822 
14,959 

1,353 
1,107 

15,621 

11,597 


268,491 
207,514 


Wage  earners 
(average 
number) 


Value  of  products 


411,575 
301,868 

1,025,044 
744,069 

1,437,258 
1,021,869 

907,514 
669,043 

237,988 

179,539 

248,785 
160,422 

415,990 
298,744 

507,311 
314,283 

309,766 
248,626 

77,827 
55,120 

342,827 
231,716 
166,810 
132,526 
40,506 
46,747 

485,845 
308,191 


6,615,046 
4,712,763 


$3,937,617,891 
2,199,203,442 

3,163,126,293 
1,818,036,771 

3,054,708,084 
1,627,889,077 

1,582,522,263 
1,004.716,682 

1,430,901,954 
726,105,558 

1,238,251,401 
688,927,152 

1,179,285,247 
607,957,231 
999,326,577 
504,969,835 

992,713,322 
582,047,900 

674,311,051 
382,898,381 

531,736,831 
270,650,143 

416,695,104 

263,713,173 

73,360,315 
74,532,277 

1,397,495,537 
655,270.079 


20,672,051,870 
11,406,926,701 


HISTORY  OF  MEAT-PACKING  INDUSTRY         385 

Food  and  kindred  products.  The  more  important  items  in  this 
group  are  slaughtering  and  meat-packing  products;  flour  and  grist 
mill  products;  butter,  cheese,  and  condensed  milk;  canned  and  pre- 
served fruits,  vegetables,  and  fish;  and  refined  sugar  (p.  382). 

The  slaughtering  and  meat-packing  industry  tends  to  keep  close 
to  the  great  stock-raising  areas  (pp.  366-368),  in  order  to  avoid  freight 
charges  on  waste  material  and  to  prevent  the  animals  losing  weight  on 
the  way  to  the  slaughtering  centers.  The  total  value  of  the  products 
of  the  industry  in  1910  was  $1,370,000,000. 

Grazing  naturally  precedes  farming  in  the  order  of  economic  development  (Why?) , 
and  as  the  chief  grazing  area  moved  westward  in  front  of  the  advancing  agricultural 
zone,  the  slaughtering  and  packing  industry  followed.  In  early  days,  stock  was 
driven  from  the  pastures  of  the  Piedmont  Plateau  to  be  killed  at  Philadelphia, 
Baltimore,  and  Charleston.  The  battle  of  Cowpens,  in  the  Revolutionary  War, 
was  so  called  because  fought  about  the  pens  of  a  Piedmont  cattle  ranch.  Later, 
great  numbers  of  cattle  and  hogs  were  driven  to  the  seaboard  from  the  settlements 
west  of  the  Appalachians  (p.  274).  After  the  War  of  181 2,  the  pork-packing  indus- 
try found  its  chief  center  in  Cincinnati,  where  it  remained  until  about  i860  (p.  276). 
During  this  period,  the  business  was  carried  on  also  at  various  other  points  on 
the  Ohio  canals  and  the  Ohio,  Mississippi,  Illinois,  Wabash,  and  other  rivers. 
By  1861-1862,  the  center  of  the  industry  had  moved  from  Cincinnati  to  Chicago, 
and  the  business  had  declined  in  many  of  the  river  towns.  Greater  economy  in 
manufacture  was  possible  in  a  small  number  of  large  establishments  than  in  a  large 
number  of  small  ones,  and  Chicago,  as  the  greatest  railroad  center,  had  unrivaled 
facilities  for  assembling  the  stock.  It  is  also  on  the  northern  edge  of  the  corn  belt 
(Fig.  259;  Why  important?),  and  within  easy  reach  of  the  great  grazing  lands. 
Chicago  still  leads  in  the  industry,  contributing  nearly  y^  of  the  total  value  of  the 
products  for  the  country,  but  the  second  and  third  centers  are  found  on  the  Missouri 
River,  at  Kansas  City  and  South  Omaha,  respectively.  The  most  important 
thing  in  the  recent  history  of  this  industry  has  been  the  more  and  more  nearly  com- 
plete use  of  the  waste  products  of  the  slaughter  houses.  Among  the  things  made 
from  these  products  are  soap,  candles,  glue,  gelatine,  glycerine,  ammonia,  knife- 
handles,  and  fertilizer. 

The  value  of  the  flour  and  grist  mill  products  of  the  United 
States  has  increased  rapidly  with  the  growth  in  the  production  of 
cereals,  and  in  1910  amounted  to  more  than  $880,000,000.  Five- 
eighths  of  the  value  of  the  output  of  these  mills  is  in  wheat  flour.  Other 
important  products  are  rye  and  buckwheat  flour,  corn  meal,  and 
feed  for  animals.  All  branches  of  the  industry  have  expanded  west- 
ward, following  the  westward  movement  of  the  centers  of  production 
of  the  great  cereal  crops  (Fig.  261).  Flour  and  grist  mills  are  distribut- 
ed widely,  for  with  the  exception  of  a  comparatively  few  large  mills, 
they  supply  local  demands  only.     Minnesota,  New  York,  Kansas, 


386  DISTRIBUTION  OF  INDUSTRIES 

Ohio,  and  Illinois  are  the  leading  flour-producing  states,  and  Minne- 
apolis is  the  leading  city  (p.  288). 

The  manufacture  of  dairy  products  in  factories  is  a  modern 
development.  Formerly,  this  work  was  done  almost  entirely  on 
the  farms.  In  185 1,  there  was  only  one  cheese  factory  in  the  United 
States;  in  1905,  there  were  more  than  3,600.  New  York,  Wisconsin, 
Iowa,  Illinois,  Minnesota,  and  Pennsylvania  are  the  six  leading  states 
in  the  industry  (p.  366).  The  value  of  factory-made  butter,  cheese, 
and  condensed  milk  exceeded  $270,000,000  in  1910. 

The  canning  and  preserving  of  foods  is  a  comparatively  new 
industry  in  the  United  States,  having  little  importance  before  1850, 
Now,  the  total  yearly  value  of  canned  fooas,  exclusive  of  meats, 
is  about  $160,000,000.  The  leading  states  in  the  industry  are  Cali- 
fornia, Maryland,  and  New  York.  The  conditions  which  determine 
the  distribution  of  the  industry  have  been  given  (p.  379). 

Iron  and  steel  and  their  products.  This  group  of  manufac- 
tures ranks  second  in  value  of  product  (p.  384).  It  comprises  37 
industries,  the  basic  ones  being  the  manufacture  of  iron  and  steel. 
Among  the  others  are  those  producing  structural  iron  work,  rails, 
machinery,  tools,  hardware,  tin  plate  (really  sheets  of  iron  coated 
with  tin),  and  various  small  products.  The  iron  and  steel  industry 
is  carried  on  in  some  27  states,  but  nearly  9/io  of  the  total  output 
comes  from  Pennsylvania,  Ohio,  Illinois,  and  Alabama. 

The  successful  use  of  hard  coal  as  fuel  gave  the  first  great  impulse  to  iron 
production,  and  located  the  iron  industry  in  eastern  Pennsylvania,  with  Phila- 
delphia the  leading  market.  About  the  close  of  the  Civil  War,  the  center  of  the 
industry  moved  to  Pittsburgh,  where  it  still  remains.  A  number  of  influences  led 
to  the  change:  (i)  The  hard  coal  of  eastern  Pennsylvania,  because  less  abundant 
and  in  great  demand  for  domestic  use,  cost  more  than  the  soft  coal  of  the  western 
part  of  the  state.  Furthermore,  coke  made  from  the  latter  was  more  efficient, 
ton  for  ton,  than  hard  coal.  (2)  The  Lake  Superior  ore  was  of  high  average  grade, 
was  mined  easily,  and  could  be  brought  to  Lake  Erie  ports  cheaply  by  lake.  (3) 
The  rapid  development  of  the  country  west  of  the  Appalachians  helped  to  bring 
about  the  change.  Although  Pittsburgh  did  not  become  the  center  of  the  industry 
until  after  the  Civil  War,  it  had  nail  factories,  foundries,  and  the  like,  before  the 
beginning  of  the  century.  As  indicated  elsewhere  (p.  282;  Fig.  198),  Lake  Superior 
iron  ore  goes  to  Pennsylvania  coal,  rather  than  the  reverse,  because  much  more  coal 
than  ore  is  needed  in  the  manufacture  of  steel,  and  because  the  ore,  in  being  sent 
to  Pittsburgh,  is  on  the  way  to  its  final  market.  Various  phases  of  the  iron  industry 
are  carried  on  less  extensively  at  other  cities  on  or  near  the  Great  Lakes,  especially 
at  Chicago  and  Cleveland,  where  ore  and  coal  can  be  brought  together  cheaply, 
and  where  market  conditions  are  good. 

In  the  South,  Birmingham,  Alabama,  is  the  leading  center  of  the  iron  and 


THE  TEXTILE   INDUSTRIES  387 

steel  industry.  In  smelting  iron  ore  it  is  mixed  with  limestone  and  coke,  and  when 
the  mixture  is  heated  in  the  furnace,  the  metal  iron  is  released  from  the  ore,  and  is 
drawn  out  into  m-olds.  At  Birmingham,  iron  ore,  coal,  and  limestone  are  found 
close  together.  This  fortunate  combination  (with  the  Southern  market)  has  made 
Birmingham  an  important  city,  and  a  leading  factor  in  the  industrial  growth  of 
the  southern  states. 

Textile  manufactures.  The  industries  of  this  group  furnish 
the  materials  for  nearly  all  our  clothing  and  for  many  household 
articles,  such  as  rugs  and  carpets,  draperies,  and  bedding.  Vegetable 
and  animal  fibers  constitute  the  raw  materials  used  by  the  44  textile 
industries.  The  principal  industries  of  the  group  are  based  on  cotton, 
wool,  and  silk.  Various  products  are  made  also  from  flax,  hemp,  and 
jute. 

The  textile  mills  of  the  United  States  consumed  in  1910  about  2,500,000,000 
pounds  of  raw  cotton,  valued  at  more  than  $290,000,000.  The  value  of  the  cotton 
manufactures  was  more  than  $620,000,000.  Southern  New  England  has  led  in 
the  manufacture  of  cotton  throughout  the  history  of  the  industry  in  the  United 
States,  but  now  its  leadership  is  threatened  seriously  by  the  South  Atlantic  states. 
New  England  has  the  advantage  of  a  much  earlier  start  in  the  industry,  and  of  a 
better  supply  of  labor  (p.  382);  but  the  southern  mills  are  very  much  nearer  the 
cotton  fields.  Both  sections  possess  abundant  water  power.  This  is  a  minor  factor 
in  New  England,  but  a  very  important  one  in  the  South. 

Woolen  manufactures  include  worsted  goods,  suiting,  blankets,  carpets,  felt 
goods,  and  wool  hats.  Much  wool  is  imported  for  the  mills,  which  consume  more 
than  500,000,000  pounds  annually.  The  leading  manufacturing  centers  are  in  the 
Middle  Atlantic  and  New  England  states. 

The  silk  mills  of  the  United  States  are  dependent  entirely  upon  foreign  coun- 
tries for  raw  material.  Mulberry  trees  could  be  grown  and  silkworms  reared  in 
this  country,  but  the  industry  requires  much  hand  labor,  and  the  cost  of  the  latter 
in  the  United  States  prevents  the  production  of  raw  silk  as  cheaply  as  it  can  be 
produced  in  southern  Europe,  Japan,  and  China.  The  leading  silk-manufacturing 
states  are  New  Jersey,  Pennsylvania,  New  York,  and  Connecticut. 

Lumber  and  its  manufactures.  The  logging  camp  and  lumber 
mill  furnish  material  for  the  23  other  branches  of  industry  included 
in  this  group.  The  fundamental  industries  have  been  discussed 
(pp.  370-372),  Among  the  products  of  the  industries  which  use  lum- 
ber are  doors,  blinds,  sash,  interior  finish,  boxes,  matches,  "wooden- 
ware,"  and  furniture  (p.  380).  Great  quantities  of  lumber  are  used 
also  in  building,  and  in  certain  industries  included  in  other  groups, 
such  as  shipbuilding  and  the  manufacture  of  carriages  and  wagons. 
Lumber  products  are  manufactured  on  a  commercial  scale  in  every 
state,  in  marked  contrast  with  the  concentration  of  certain  of  the 


388  DISTRIBUTION  OF  INDUSTRIES 

other  greater  industries,  such  as  the  manufacture  of  iron  and  steel 
and  textiles. 

Chemicals  and  allied  products.  This  group  contains  many 
manufactures  which  serve  a  wide  variety  of  purposes.  Among  the 
products  are  paints  and  varnishes,  dyestuffs,  bleaching  materials, 
medicines,  druggists'  preparations,  baking  powder,  glue,  soap,  ink, 
various  oils,  explosives,  and  fertilizers.  Naturally,  such  diverse  com- 
modities are  manufactured  in  many  different  places,  but  more  than 
half  the  products  of  the  group  as  a  whole  come  from  Pennsylvania, 
New  York,  New  Jersey,  Ohio,  and  Illinois. 

Metals  and  metal  products  other  than  iron  and  steel.  Many 
things  are  made  of  gold,  silver,  copper,  lead,  and  zinc  (pp.  181-182), 
such  as  jewelry,  watches,  clocks,  silverware,  brassware,  and  pins. 
Many  of  the  34  classes  of  industry  belonging  to  this  group  are  carried 
on  extensively  in  the  northeastern  states,  especially  southern  New 
England.  The  chief  advantages  enjoyed  by  this  section  in  these 
industries  are  (i)  an  early  start,  and  (2)  the  services  of  skilled  work- 
ers, more  numerous  there  than  elsewhere  during  the  early  develop- 
ment of  these  industries. 

Paper  and  printing.  Printing  and  publishing  are  the  most 
important  and  most  widely  distributed  industries  of  this  group, 
which  includes  also  the  manufacture  of  wood-pulp,  paper  of  all 
kinds,  paper  bags  and  boxes,  etc. 

The  principal  centers  of  the  wood-pulp  industry  have  been  noted  (p.  380). 
The  output  of  paper  boxes  has  increased  rapidly  during  recent  years;  largely  be- 
cause of  the  increasing  cost  ot  wood,  many  things  are  now  put  up  in  paper  boxes 
which  formerly  were  packed  in  wooden  boxes.  The  annual  per  capita  value  of  the 
output  in  the  printing  and  publishing  business  is  more  than  ten  times  greater 
than  it  was  in  1850.  This  significant  change  reflects  in  part  the  progress  made  in 
education,  the  reduced  cost  of  reading  matter,  and  the  greater  facilities  for  its 
distribution,  such  as  rural  free  deUvery.  In  1905,  the  value  of  the  products  of 
printing  and  pubhshing  in  six  states  —  New  York,  Illinois,  Pennsylvania,  Massa- 
chusetts, Ohio,  and  Missouri  —  amounted  to  Vi  that  for  the  entire  country. 

Vehicles  for  land  transportation.  The  operations  of  the  repair 
shops  of  steam  railroad  companies,  the  manufacture  of  carriages 
and  wagons,  and  the  manufacture  of  steam  railroad  cars  are  the 
most  important  of  the  11  industries  comprising  this  group.  In 
recent  years  the  output  of  bicycles  has  declined  rapidly,  while  that 
of  automobiles  and  motorcycles  has  increased  enormously. 

The  value  of  the  automobiles  made  in  1900  was  less  than  $5,000,000;  in  191^ 
about  $165,000,000.     In  1905, automobiles  were  manufactured  in  17  states,  with 


LEATHER  PRODUCTS  AND   LIQUORS  389 

Michigan,  Ohio,  New  York,  and  Connecticut  leading.  The  value  of  those  made 
in  Detroit  is  more  than  y^  of  the  total  for  the  industry.  The  leadership  of 
Detroit  appears  to  be  due  to  the  impetus  resulting  from  the  success  of  the  first 
factories  estabUshed,  rather  than  to  superior  natural  advantages. 

Leather  and  its  finished  products.  The  basic  industry  in  this 
group  is  tanning,  while  the  dependent  industries  include  the  manu- 
facture of  leather  products  of  all  kinds.  Of  the  latter,  the  boot  and 
shoe  industry  is  most  important,  but  large  quantities  of  leather 
are  used  in  making  harnesses,  saddles,  trunks,  bags,  furniture,  gloves, 
mittens,  and  belting,  in  binding  books,  and  in  other  ways.  For 
many  years  Massachusetts  has  been  the  leading  shoe-manufacturing 
state  (p.  383),  but  the  industry  is  growing  rapidly  at  various  points 
in  the  middle  states. 

In  the  past,  the  tanning  industry  has  depended  chiefly  on  local  supplies  of 
tannic  acid,  obtained  usually  from  the  bark  of  oak  or  hemlock,  and  as  the  supply 
of  bark  failed  in  one  area,  the  industry  developed  in  another.  The  business  is  now 
important  in  Pennsylvania,  Michigan,  and  Wisconsin.  Until  recently,  the  industry 
was  attended  by  an  enormous  waste  of  timber;  trees  were  felled  by  thousands, 
from  which  only  the  bark  was  taken  for  the  tanneries,  the  logs  being  left  to  rot  in 
the  woods. 

Liquors  and  beverages.  The  value  of  these  products  increased 
more  than  /^i  between  1900  and  1910,  amounting  to  more  than  $590,- 
000,000  in  the  latter  year.  Illinois  leads  the  states  in  making  dis- 
tilled liquors,  while  Indiana,  Ohio,  and  Kentucky  follow  in  the  order 
named.  New  York,  Pennsylvania,  Wisconsin,  Missouri,  and  Illinois 
are  the  leading  states  in  the  production  of  malt  liquors.  California, 
New  York,  and  Ohio  lead  in  wine-making. 

Peoria,  Illinois,  ranks  first  among  American  cities  in  the  manufacture  of 
distilled  liquors.  It  attained  leadership  in  the  liquor  industry  largely  because  of 
(i)  its  central  location  in  the  corn  belt  of  the  state;  (2)  its  transportation  facilities, 
which  enable  it  to  collect  at  low  freight  rates  the  surplus  grain  of  the  surrounding 
area;  and  (3)  an  abundant  supply  of  cheap  coal  from  nearby  mines.  The  manu- 
factured product,  owing  to  its  relatively  small  bulk  and  large  value,  can  bear  the 
cost  of  transportation  to  distant  markets.  Nearness  to  the  grain  supply  has  also 
been  an  important  factor  in  the  manufacture  of  malt  liquor  in  Milwaukee,  Chicago, 
St.  Louis,  Cincinnati,  and  St.  Paul. 

Clay,  glass,  and  stone  products.  Some  of  the  industries  of 
this  group  have  been  noted  sufficiently  in  earlier  connections  (pp. 
175-176,  266).  Clay  products  are  used  most  in  the  building  trades, 
and  their  consumption  is  increasing  rapidly.  Ohio,  Pennsylvania, 
New  Jersey,  Illinois,  and  New  York  lead  in  clay  products.  Pennsyl- 
vania, Indiana,  and  Ohio  lead  in  the  manufacture  of  glass. 


Sgo  DISTRIBUTION  OF  INDUSTRIES 

Deposits  of  quartz  sand,  the  only  raw  material  which  enters  into  all  kinds  of 
glass,  are  widespread,  but  the  making  of  glass  on  a  large  scale  is  fairly  well  localized 
because  of  the  need  of  satisfactory  fuel  for  the  work.  With  good  fuel,  a  skillful 
glass-maker  can  make  fairly  good  glass  from  inferior  material,  but  with  poor  fuel 
he  cannot  make  good  glass  with  the  best  materials.  Gas  is  the  ideal  fuel  in  glass- 
making,  because  it  is  cleanest,  and  gives  intense,  uniform  heat  under  perfect 
control.  The  leading  states  in  the  industry  attained  that  position  largely  because 
of  their  supplies  of  natural  gas. 

Tobacco  products.  These  include  cigars,  cigarettes,  chewing 
and  smoking  tobacco,  and  snufiF.  The  value  of  the  products  increased 
from  $31,000,000  in  i860  to  $416,  000,000  in  1910. 

The  manufacture  of  cigars  is  distributed  widely,  Pennsylvania,  New  York,  and 
Ohio  leading.  More  than  4/5  of  the  total  output  of  cigarettes  are  made  in  New 
York  and  Virginia.  Missouri,  North  Carolina,  Kentucky,  and  Virginia  lead  in 
the  production  of  chewing  and  smoking  tobacco. 

Shipbuilding.  Since  1850,  the  value  of  the  products  of  this 
industry  has  increased  nearly  fourfold  and  the  capital  invested 
twenty-one  fold.  The  latter  fact  means  that,  as  iron  and  steel  steam- 
ships replaced  wooden  sailing  vessels,  much  more  capital  was  required 
than  when  ships  were  built  of  wood  only.  The  need  of  greater  capital 
helped  to  bring  about  the  concentration  of  shipbuilding  in  large 
establishments,  with  the  result  that  there  were  only  about  half  as 
many  establishments  in  1905  as  in  1880.  New  York,  Pennsylvania, 
Virginia,  New  Jersey,  and  Massachusetts  are  the  leading  shipbuilding 
states  on  the  Atlantic  coast;  Ohio  and  Michigan  lead  on  the  Great 
Lakes;  and  California  and  Washington  on  the  Pacific  coast. 

The  rapid  growth  in  recent  years  of  the  shipbuilding  industry  on  the  Great 
Lakes  has  been  due  to  the  demand  created  by  the  enormous  increase  in  the  com- 
merce of  the  lakes  (pp.  279,  282).  At  the  same  time,  of  course,  the  development  of 
shipbuilding  has  favored  the  continued  growth  of  lake  transportation.  The  ship- 
yards at  West  Bay  City,  Michigan,  and  West  Superior,  Wisconsin,  are  outgrowths 
of  the  wooden  shipbuilding  industry.  Those  at  or  near  Buffalo,  Lorain,  Cleveland, 
Toledo,  Detroit,  and  South  Chicago  are  located  conveniently  with  reference  to 
the  great  steel  mills. 

Miscellaneous  industries.  There  are  65  industries  of  varying 
importance  carried  on  in  the  United  States  which  cannot  be  classed 
properly  with  any  of  the  other  groups.  The  combined  value  of  their 
products  in  1910  was  more  than  $1,400,000,000.  Among  the  indus- 
tries of  the  group  whose  products  are  of  greater  value  are  the  manu- 
facture of  agricultural  implements  (p.  382);  ammunition;  brooms 
and  brushes;  buttons;  coke  (p.  386);  electrical  machinery,  apparatus. 


QUESTIONS  39i 

and  supplies;  fur  goods;  ice;  mattresses  and  spring-beds;  musical 
instruments;  photographic  materials  and  apparatus;  and  rubber  and 
elastic  goods. 

Questions 

1.  (i)  Explain  the  fact  that  the  shores  of  Chesapeake  Bay,  Long  Island,  and 
Lake  Michigan  (east  shore)  were  among  the  first  sections  to  grow  vegetables  on 
a  large  scale  for  city  markets.  (2)  Why  is  the  business  more  important  on  the 
east  shore  of  Lake  Michigan  than  on  the  west  shore? 

2.  Formerly  strawberries  were  grown  extensively  in  a  few  places  only,  as  in 
parts  of  Maryland,  New  York,  Ohio,  and  western  Michigan.  Now  they  are  grown 
on  a  large  scale  in  Florida,  Tennessee,  Arkansas,  Missouri,  and  other  states,  (i) 
Explain  the  relatively  early  development  of  the  business  in  the  first-mentioned 
states.     (2)  What  permitted  its  later  development  in  the  other  states? 

3.  It  is  estimated  that  the  forests  of  the  United  States  (Fig.  271)  contain  about 
the  following  percentages  of  their  original  stand  of  timber:  Northern  Forest, 
30  per  cent;  Hardwood  Forest,  21  per  cent;  Southern  Forest,  50  per  cent;  Rocky 
Mountain  Forest,  75  per  cent;  Pacific  Forest,  79  per  cent.     Why  the  differences? 

4.  What  advantages  have  made  New  Jersey  a  great  manufacturing  state 
(6  th  in  19 10),  in  spite  of  the  fact  that  it  has  small  fuel  and  water-power  resources, 
and  produces  relatively  little  of  the  raw  material  used  by  its  factories? 

5.  Explain  the  fact  that  in  Nebraska  most  of  the  manufacturing  is  done  in 
the  eastern  part  of  the  state  (more  than  Vs  of  it  in  two  coimties),  while  in  Iowa 
it  is  distributed  rather  evenly  throughout  the  state. 

6.  Among  the  leading  manufactures  of  Chicago  are  meat  products,  men's 
clothing,  foundry  and  machine  shop  products,  iron  and  steel,  the  products  of 
printing  and  publishing  houses,  and  railroad  cars.  What  advantages  has  Chicago 
for  carrying  on  each  of  these  industries? 

7.  Compare  and  contrast  the  general  advantages  for  manufacturing  of  (i) 
Massachusetts  and  Texas,  and  (2)  Utah  and  Ohio. 

8.  Flour  and  sugar  are  household  necessities,  (i)  Explain  why  the  former 
is  made  in  thousands  of  mills  throughout  the  country,  and  the  latter  at  compara- 
tively few  points.  (2)  Will  the  situation  with  regard  to  sugar  change  in  the  future? 
Why? 

9.  Why  does  West  Virginia  rank  low  (29th)  as  a  manufacturing  state,  although 
it  mines  much  coal  (second  coal-producing  state  in  1910)? 

10.  Explain  the  fact  that  the  section  east  of  the  Mississippi  River  and  north 
of  the  Ohio  and  Potomac  rivers  contributes  about  ^  of  the  total  value  of  man- 
ufactured products  for  the  United  States. 


CHAPTER  XXI 
DISTRIBUTION   OF  POPULATION;     DEVELOPMENT   OF  CITIES 

Factors  Affecting  Density 

As  we  have  seen,  the  distribution  and  density  of  population  are 
influenced  by  many  factors  —  such  as  topography,  climate,  soil, 
natural  resources,  transportation  facilities,  and  the  occupations  of  the 
people.  The  influence  of  these  factors  may  be  reviewed  by  consider- 
ing briefly  the  expansion  and  present  distribution  of  population  in 
the  United  States. 

Fig.  276  shows  the  distribution  of  population  in  1790,  when  the 
first  census  was  taken.  Nearly  all  the  people,  emigrants  from 
Europe,  were  still  east  of  the  Appalachian  Mountains.  This  was 
due  largely  to  the  difficulty  of  crossing  the  mountain  barrier,  the 
privations,  dangers,  and  difficulties  of  life  in  the  Interior,  and  the 
desirability  of  being  near  the  Atlantic  Ocean  or  some  navigable  river 
flowing  into  it,  for  purposes  of  trade.  Furthermore,  the  lands  east 
of  the  mountains  and  along  the  Great  Appalachian  Valley  had  been 
sufficient  for  the  needs  of  the  settlers  until  a  few  years  before  (about 

1775)- 

In  New  England,  the  population  was  densest  toward  the  south  and  south- 
east. This  is  explained  by  the  colder  climate  at  the  north;  the  rough  uplands 
there,  infertile  in  many  places;  the  fact  that  few  of  the  rivers  served  as  good  high- 
ways far  into  the  interior  (Why?) ;  and  the  importance  of  sea-interests  (fishing, 
shipbuilding,  the  carrying  trade)  in  New  England  hfe.  The  influence  of  the 
Connecticut  Valley  and  the  Champlain  lowland  on  the  distribution  of  the  frontier 
population  is  interesting.  In  New  York ,  most  of  the  people  were  in  or  near  the  Hudson 
and  Mohawk  valleys,  which  had  fertile  soils  in  many  places,  and  afforded  easy  com- 
munication with  New  York  City.  The  Adirondacks  and  Catskills  were  almost  unin- 
habited. The  sandy,  forested  coastal  plain  of  southeastern  New  Jersey  had  a  sparse 
population,  while  a  strip  of  denser  settlement  extended  across  the  state  between 
Philadelphia  and  New  York  City.  (Why?  Compare  with  Figs.  278  and  281.) 
In  the  Carolinas  the  Piedmont  Plateau,  with  its  relatively  small  farms,  had  a 
denser  population  than  parts  of  the  Coastal  Plain,  with  its  big  plantations.  The 
influence  of  the  Great  Appalachian  Valley  is  shown  by  the  settled  strip  which 
extended  southwest  from  Virginia.    The  settled  area  in  southwestern  Pennsyl- 

392 


THE  UNITED  STATES  IN  1790 


393 


45t 


43^; 


41^ 


39i 


37- 


35- 


33—' 


31^^ 


>7- 


^ 


8   ^ 


Nils     H 


>J-Center  of  Population 
39°  16.6  N.    76°  11.2' W. 

Under  2  inhab.  to  the  Sq.  Mile  |  | 

2-6     "       " 

6-18     "        " 

18-45     "        " 

45-90     "        " 

90  and  over  " 


v*! 


1. 


-351J 


33- 


-25- 


83° 


79" 


Fig.  276.    Map  showing  distribution  of  population  in  the  United  States  in  1790. 


394 


DISTRIBUTION  OF  POPULATION 


vania  reflects,  in  part,  the  attractions  of  the  Monongahela  Valley  and  some  of 
its  tributaries.  The  large  area  of  settlement  in  north-central  Kentucky  was  the 
famous  "Blue  Grass  Region."  Here  were  rich  soils,  salt  springs  (p.  183),  and 
navigable  streams.  The  settlers  of  central  Tennessee  were  also  in  a  region  of  fertile 
soils,  and  used  the  Cumberland  River  as  a  highway.  The  rough  plateau  lands  of 
eastern  Tennessee,  Kentucky,  and  West  Virginia  had  few  settlers,  or  none  at  all. 

After  1790  population  spread  rapidly  toward  the  west  (Fig.  277), 
especially  along  such  highways  as  the  Ohio  River  and  (later)  the 
Great  Lakes  (p.  281).  The  population  map  for  1820  (Fig.  278) 
shows  strikingly  the  influence  of  geographic  features.  The  Adiron- 
dack Mountains  and  the  less  accessible  parts  of  the  Appalachian 
Mountains  and  the  Alleghany  Plateau  remained  uninhabited  wil- 


■/910  ^)89g- 


Fig.  277.    Map  showing  the  center  of  population  in  the  United  States  at  each 
census,  1790  to  1910. 


dernesses.  On  the  other  hand,  most  of  the  fertile  lowlands  favorably 
situated  and  available  for  settlement  had  been  occupied.  The 
most  striking  feature  of  the  western  frontier  was  the  control  of 
settlement  by  the  larger  rivers,  which  were  the  chief  highways  of  the 
time  (pp.  274-276).  Each  one  (the  Red,  Arkansas,  Missouri,  Missis- 
sippi, and  others)  was  bordered  for  some  distance  by  a  narrow  settled 
area,  while,  for  the  most  part,  the  tracts  between  were  still  unoccu- 
pied. The  influence  of  routes  from  the  East  is  illustrated  by  the 
belt  of  settlement  extending  from  western  New  York  around  the 
southern  shore  of  Lake  Erie  to  Lake  St.  Clair.  The  presence  of 
Indians  explains  some  of  the  blank  areas  on  the  map  within  the 
generally  settled  region,  as  in  Georgia,  Alabama,  central  and  northern 
Mississippi,  and  western  Tennessee.  After  the  removal  of  the 
Indians,  these  areas  were  settled  quickly. 

The  vmsettled  condition  of  northwestern  Ohio  was  due  partly  to  the  "Great 
Black  Swamp."  The  lower  part  of  the  Mississippi  delta  and  some  of  the  lands 
along  the  Gulf  coast  also  were  unoccupied  because  swampy-  For  some  years, 
settlers  avoided  the  prairies  of  the  northern  Interior.  They  were  thought  infertile 
(P-  i73)>  timber  must  be  had  for  buildings,  fences,  and  fuel;  they  did  not  afford 


DISTRIBUTION  OF  PEOPLE  IN   1820 


395 


Fig.  278.    Map  showing  distribution  of  population  in  the  United  States  in  1820. 


396 


DISTRIBUTION  OF  POPULATION 


THE  WEST  IN  1880  397 

enough  running  water  for  stock  or  mills;  there  was  little  protection  from  the 
bitter  winds  of  winter;  and  the  farmers  did  not  know  how  to  "break"  and  work 
the  tough  prairie  sod.  The  gradual  conquest  of  the  prairies  is  one  of  the  most 
interesting  phases  of  the  settlement  of  the  region.  The  dense  forests  in  the  north- 
ern Lake  region  helped  for  years  to  keep  farmers  away  from  large  areas. 

The  appearance  of  the  railroad  introduced  a  new  and  powerful 
factor  in  the  expansion  of  population.  The  first  American  railroad 
was  built  in  Massachusetts  in  1826.  By  the  early  1850 's,  railroads 
had  been  built  across  the  Appalachian  Mountains  from  the  leading 
seaports  of  the  Northeast.  In  1853  Chicago  was  connected  by  rail 
with  New  York  City.  The  Mississippi  River  was  reached  shortly 
after,  and  in  1869  the  first  railroad  was  completed  to  the  Pacific. 
The  railroads  opened  up  vast  areas  for  settlement  which  had  not  been 
available  before.  This  was  particularly  true  of  large  areas  west  of 
the  Mississippi,  whose  settlement  and  development,  in  the  absence 
of  navigable  waterways,  had  to  await  the  railroad.  Fig.  279  shows 
the  present  railroad  web. 

By  1880,  many  parts  of  the  West  were  settled  (Fig.  280),  Fertile 
soils  had  favored  farming  along  the  bases  of  some  of  the  mountains 
and  in  many  valleys,  the  discovery  of  mineral  deposits  had  attracted 
thousands  of  prospectors  and  miners  to  various  places,  and  the  graz- 
ing industry  supported  a  sparse  population  over  wide  areas. 

The  settlements  in  the  Black  Hilis  (Fig.  280)  were  the  result  of  the  recent 
discovery  there  of  gold.  Most  of  the  settlers  in  central  and  western  Montana 
were  farmers,  located  chiefly  in  the  valleys  of  the  larger  streams.  Besides  the 
farmers,  there  were  some  miners.  In  Colorado  there  were  farmers  (i)  along  the 
east  base  of  the  Rocky  Mountains,  where,  at  many  points,  irrigation  was  possible, 
and  (2)  in  some  of  the  mountain  valleys.  In  addition,  a  large  mining  population 
had  been  attracted  by  the  discovery,  a  few  years  before,  of  rich  deposits  of  gold, 
silver,  and  lead  in  the  Leadville  district  (p.  315).  In  New  Mexico,  the  Rio  Grande, 
Rio  Pecos,  and  upper  Canadian  valleys  had  drawn  many  settlers.  In  Utah,  the 
agricultural  settlements  of  the  Mormons  e.xtended  along  the  base  of  the  Wasatch 
Mountains,  where  there  were  fertile  and  irrigable  soils  (p.  291).  The  principal 
agricultural  settlements  in  Nevada  were  in  the  Humboldt  Valley  and  along  the 
Central  Pacific  Railroad.  The  other  settlements  of  the  state  depended  chiefly 
on  mining.  In  California,  the  commercial  advantages  of  San  Francisco  Bay  had 
attracted  many  people,  and  some  of  the  gold-producing  districts  were  well  settled. 
The  great  central  valley  and  the  more  inviting  valleys  of  the  Coast  Range  were 
occupied  by  farmers. 

The  lowlands  west  of  the  Cascade  Mountains  in  Oregon  and  Washington  were 
occupied  for  the  most  part,  while  in  the  drier  regions  east  of  those  mountains  most 
of  the  settlements  were  near  the  Columbia  River  and  its  tributaries.  The  remain- 
ing population  of  the  West  was  scattered  widely  at  military  posts,  mining  camps, 
and  on  cattle  ranches. 


598 


DISTRIBUTION  OF  POPULATION 


Fig.  280.     Map  showing  distribution  of  population  in  the  West  m  1880. 


DISTRIBUTION  OF  PEOPLE  IN   1900  399 

The  population  map  for  1900  (Fig.  281)  will  be  understood  readily 
in  the  light  of  the  preceding  discussion,  and  only  its  larger  features 
need  be  noted  here.  The  population  of  the  eastern  half  of  the 
country  was  seven  times  as  great  as  that  of  the  western  half.  The 
relatively  sparse  population  of  the  western  half  was  due  chiefly  to 
prevailing  aridity  and  the  great  extent  of  mountains  and  plateaus. 
Furthermore,  many  of  the  settled  areas  were  occupied  only  recently. 
The  relation  of  precipitation  to  population  is  suggested  by  the  fact 
that  only  about  V30  of  the  people  were  in  regions  where  precipitation 
is  less  than  20  inches.  Similarly,  the  relation  of  altitude  to  popula- 
tion is  shown  by  the  fact  that  more  than  95  per  cent  of  the  population 
lived  at  elevations  of  less  than  2,000  feet.  Since  1900,  the  population 
of  many  parts  of  the  West  has  grown  rapidly  because  of  the  develop- 
ment of  irrigation,  dry-farming,  and  mining,  and  the  growth  of  com- 
mercial and  industrial  centers.  The  greatest  densities  (Fig.  281)  are 
found  in  the  northeastern  quarter  of  the  country.  This  region  in- 
cludes much  of  the  glaciated  area,  with  its  highly  productive  soils ;  is 
unrivaled  in  its  transportation  facilities  (Fig.  279);  possesses  vast 
resources  in  timber,  in  iron,  coal,  copper,  and  other  useful  minerals; 
and  contains  most  of  the  great  commercial  and  industrial  centers 
of  the  country. 

Cities 

Cities  have  increased  rapidly  in  the  United  States,  both  in  num- 
ber and  size.  In  1850,  12.5  per  cent  of  the  total  population  of  the 
country  lived  in  the  85  cities  which  had  8,000  or  more  people  each; 
by  1900  the  percentage  of  the  population  living  in  such  cities  had 
increased  to  32.4,  and  the  number  of  such  cities  to  517.  Nearly  half 
of  the  people  of  the  country  now  live  in  villages  and  cities  of  more 
than  2,500  inhabitants.  The  increasing  proportion  of  the  population 
in  cities  has  been  due  chiefly  to  the  growth  of  urban  commerce  and 
industries  (p.  383).  The  region  with  most  cities  is  east  of  the 
Missouri  River,  and  north  of  the  Ohio  and  Potomac  rivers.  Here 
are  35  of  the  50  cities  which,  in  19 10,  had  a  population  greater  than 
100,000. 

The  leading  types  of  cities  are  (i)  commercial  cities,  (2)  manu- 
facturing cities,  (3)  mining  cities,  (4)  political  centers,  and  (5)  health 
or  pleasure  resorts.  Most  large  cities  are  both  commercial  and 
industrial  centers,  while  some  belong  also  in  varying  degree  to  one 
or  more  of  the  other  classes. 


400 


DISTRIBUTION  OF  POPULATION 


s:     V     3    o 


^      /2  c 


THE  RISE  OF  COMMERCIAL  CITIES  401 

Commercial  cities.  Cities  dependent  chiefly  on  commerce 
grow  up  (i)  where  conditions  favor  the  collection  and  distribution  of 
commodities  on  a  large  scale,  or  (2)  on  important  lines  of  communica- 
tion at  points  where  the  mode  of  transportation  is  changed.  Such 
places  are  (i)  seaports,  (2)  river  ports,  (3)  lake  ports,  and  (4)  railroad 
centers. 

(i)  The  growth  of  seaport  cities  is  influenced  mainly  by  (a) 
their  position  in  relation  to  great  trade  routes;  (b)  the  size,  resources, 
population,  and  accessibility  of  their  tributary  areas  {hinterlands); 
and  (c)  the  character  of  their  harbors.  The  ideal  harbor  is  large 
enough  to  contain  many  vessels,  deep  enough  to  admit  the  largest 
ships,  protected  from  storms,  free  from  ice,  connected  with  the  open 
sea  by  a  deep  channel,  and  has  shores  of  such  a  kind  as  to  facilitate 
the  building  of  docks  and  the  handling  of  freight  (p.  350).  Com- 
mercial cities  are  likely  to  grow  up  at  or  near  the  mouths  of  navigable 
rivers,  for  the  latter  serve  as  highways  into  the  interior,  and  in  many 
cases  afford  good  harbors.  When  the  lower  courses  of  rivers  have  deep 
channels,  such  cities  may  be  some  distance  upstream,  nearer  the 
heart  of  the  country.  Thus  Montreal,  more  than  800  miles  inland, 
is,  in  effect,  a  seaport. 

San  Francisco  has  a  fine  harbor  (Fig.  242),  but  trade  with  countries  across 
the  Pacific  has  been  relatively  unimportant;  high  mountains  separate  it  from  the 
interior;  and  to  the  east  of  these  mountains  stretch  broad  deserts  with  sparse 
populations.  For  years  Boston,  Philadelphia,  and  Baltimore,  having  good  harbors 
and  local  hinterlands  of  importance,  rivaled  New  York  City  in  commercial  im- 
portance. But  the  Hudson-Mohawk  depression  gave  New  York  the  best  connec- 
tions with  the  interior,  and  the  opening  of  the  Erie  Canal  (p.  286)  added  the  Great 
Lakes  Region  to  its  hinterland,  enabling  it  to  leave  the  others  behind. 

(2)  Since  water  transportation  preceded  railway  transportation, 
most  early  inland  cities  are  located  at  strategic  points  on  navigable 
waterways,  (a)  At  the  head  of  river  navigation  goods  are  trans- 
ferred from  water  to  land,  or  vice  versa,  for  further  distribution, 
and  hence  commercial  towns  develop.  Thus  Haverhill  grew  up  at 
the  head  of  navigation  on  the  Merrimac,  Hartford  on  the  Connecti- 
cut, Albany  on  the  Hudson,  Augusta  on  the  Savannah,  and  St.  Paul 
on  the  Mississippi,  (b)  River  cities  are  found  also  at  the  junctions 
of  large  rivers,  for  such  places  are  focal  points  for  trade.  Here 
traffic  coming  upstream  is  divided,  a  part  going  up  each  stream, 
while  in  many  cases  freight  descending  the  tributary  streams  is 
transferred    to    boats    operating    on    the    main   river.      Pittsburgh 


402  DISTRIBUTION  OF  POPULATION 

(p.  276),  Cairo,  St.  Louis  (p.  277),  and  Vicksburg  areexamples  of  places 
whose  earlier  growth,  at  least,  was  aided  by  their  position  near  the 
junction  of  important  streams,  (c)  A  decided  change  in  the  direc- 
tion of  a  river 's  course  means  a  division  of  traffic  and  a  change  in  the 
mode  of  carriage  (Why?).  Cincinnati  (p.  276),  Nashville,  and 
Kansas  City  benefited  from  their  positions  on  great  bends  of  rivers. 
Kalamazoo,  Michigan,  and  South  Bend,  Indiana,  are  types  of  many 
smaller  places  situated  similarly,  (d)  Falls  or  rapids  may  give  rise 
to  a  commercial  city,  for  river  freight  must  be  unloaded,  carried 
around  the  obstruction,  and  either  reloaded  or  forwarded  by  land. 
The  falls  (rapids)  of  the  Ohio  made  Louisville,  those  of  St.  Mary's 
River  gave  rise  to  Sault  Ste.  Marie,  and  the  growth  of  Buffalo  was 
aided  by  the  falls  and  rapids  of  the  Niagara. 

(3)  All  the  more  important  cities  ranged  along  the  Great  Lakes 
started  as  commercial  towns  —  as  centers  of  exchange  and  trans- 
fer —  and  their  commercial  activities  still  dominate.  As  noted 
elsewhere  (p.  279),  their  exact  location  was  determined  in  most 
cases  by  natural  lines  of  communication  leading  from  the  shores  of 
the  lakes. 

Chicago  became  the  greatest  lake  port  because  of  its  superior  geographic 
advantages,  (i)  It  is  near  the  head  of  Lake  Michigan,  which  extends  farther  than 
the  other  lakes  into  the  heart  of  the  country.  (2)  It  is  located  more  centrally  than 
its  rivals  with  reference  to  the  richer  areas  of  glacial  soil  and  the  areas  leading  in 
the  production  of  corn  (Fig.  259),  wheat  (Fig.  260),  swine  (Fig.  269),  and  cattle 
(Fig.  267).  (3)  All  land  traflic  from  the  Northwest  to  the  eastern  part  of  the 
country  must  pass  around  Lake  Michigan,  and  is  therefore  tributary  to  Chicago. 
The  latter  is  accessible  also  by  land  from  the  south  and  east,  from  which  directions 
many  railroads  have  been  built  to  Chicago  to  meet  the  traffic  of  the  West  and 
Northwest.  Because  of  its  strategic  position,  Chicago  is  the  greatest  railroad 
center  in  the  world  (Fig.  279). 

The  importance  of  water  transportation  to  the  growth  of  the 
leading  cities  of  the  country  is  shown  by  the  fact  that  of  the  28 
cities  having  in  1910  a  population  of  more  than  200,000,  23  are  on 
navigable  waters.  Of  the  23,  10  are  seaports,  7  are  on  the  Mississippi 
System,  and  5  are  on  the  Great  Lakes. 

(4)  All  the  important  seaports,  river  ports,  and  lake  ports  of  the 
United  States  are  also  more  or  less  important  as  railroad  centers.  There 
are  also  a  number  of  large  cities  without  water  transportation,  like  In- 
dianapolis, which  now  owe  their  commercial  importance  largely  or 
wholly  to  the  fact  that  they  are  at  the  junction  of  several  railroad 
lines.    The  greater  cities  of  the  United  States  had  become  important 


INDUSTRIAL  AND   MINING  CITIES  403 

because  of  their  natural  advantages,  before  the  appearance  of  rail- 
roads. Railroads  were  built  to  them  to  share  in  existing  trade,  which 
they  later  helped  to  increase.  On  the  other  hand,  the  extension  of 
railroads  throughout  the  country  caused  a  multitude  of  small  cities 
and  villages  to  spring  up  on  sites  without  natural  advantages.  Such 
places  serve  as  collecting  and  distributing  points  for  the  surrounding 
country,  and,  if  railway  junctions,  they  derive  more  or  less  benefit 
from  the  resulting  exchange  and  transfer  of  traffic. 

While  the  more  important  conditions  which  give  rise  to  com- 
mercial centers  have  been  mentioned,  villages  and  cities  may  grow 
up  at  critical  points  on  lines  of  communication  for  reasons  not  men- 
tioned above.  Thus  a  ford  or  ferry  on  a  river  may  locate  a  town. 
Harrisburg,  Pennsylvania,  developed  from  Harris'  Ferry,  where  a 
land  route  toward  the  west  crossed  the  Susquehanna  River ;  Zanesville, 
Lancaster,  and  Chillicothe,  Ohio,  grew  up  where  an  important  early 
road  (Zane's  Trace)  crossed  the  Muskingum,  Hocking,  and  Scioto 
rivers.  Again,  a  mountain  pass  upon  which  trade  routes  focus  may 
give  rise  to  a  city.  Cumberland,  Maryland,  has  grown  up  in  front 
of  Wills  Creek  Water-Gap,  important  since  the  colonial  period 
(p.  232).  The  growth  of  Denver  has  been  stimulated  by  its  relation 
to  several  of  the  passes  in  the  Rocky  Mountains. 

Manufacturing  cities.  Most  large  commercial  cities  are  im- 
portant also  as  manufacturing  centers  (p.  383),  for  their  transportation 
facilities  make  it  easy  to  get  raw  materials  together  and  to  ship  out 
the  manufactured  products.  Labor,  too,  is  abundant.  New  York, 
the  commercial  metropolis  of  the  country,  leads  also  in  manufacturing; 
Chicago,  the  leading  inland  commercial  city,  is  the  second  industrial 
center;  and  Philadelphia,  the  fourth  commercial  center,  is  third  in 
industry.  On  the  other  hand,  all  industrial  cities  are  necessarily, 
in  varying  degree,  trade  centers.  In  most  cities,  therefore,  commercial 
and  industrial  activities  are  united  in  varying  proportions  determined 
largely  by  geographic  conditions.  The  factors  which  control  the 
distribution  of  manufacturing  industries  (pp.  379-383)  control  also 
the  location  of  the  cities  to  which  those  industries  may  give  rise. 
Most  distinctly  industrial  cities  are  located  in  response  to  (i)  power 
resources,  like  many  of  the  New  England  cities  (p.  381),  or  (2)  raw 
materials,  like  Birmingham,  Alabama. 

Mining  cities.  Many  villages  and  cities,  especially  in  the 
West,  have  developed  from  camps  about  mines.  As  the  mining 
industry  in  a  given  locality  grew,  tents  gave  place  to  buildings  of 


404  DISTRIBUTION  OF  POPULATION 

wood  and  brick,  business  and  professional  men  appeared  to  supply 
the  needs  of  the  miners,  and  busy  settlements  resulted,  which  in 
many  cases  became  cities  in  a  few  years.  Scranton  (Pennsvlvania), 
Joplin  (Missouri),  Deadwood  (South  Dakota),  Cripple  Creek  (Colo- 
rado), Butte  (Montana),  and  Placerville  (California)  are  types  of  a 
large  number  of  cities  and  towns  which  have  grown  up  solely  because 
of  the  wealth  of  adjacent  mines. 

Many  cities  at  which  there  are  no  mines  depend  largely  on  the 
mining  industry.  Thus  Pueblo  (Colorado)  and  Anaconda  (Mon- 
tana) were  founded  chiefly  for  extracting  metals  from  ores.  Sacra- 
mento and  Denver  first  became  important  as  outfitting  and  supply 
stations  for  nearby  mines.  Indeed,  there  are  few  cities  in  the  far 
West  which  have  not  been  influenced  by  the  mining  industry. 

Political  centers.  Few  cities  are  merely  political  centers, 
for  even  though  founded  as  such,  their  growth  is  almost  certain  to 
attract  commercial,  if  not  industrial,  enterprises.  Washington, 
D.  C,  is  a  striking  exception.  In  locating  state  capitals,  acces- 
sibility for  the  majority  of  the  people  has  been  a  leading  considera- 
tion. In  states  having  a  fairly  uniform  distribution  of  population 
and  equal  facilities  for  travel,  the  capital  tends  toward  the  geographic 
center.  Thus  the  capital  of  Illinois  shifted  from  Kaskaskia  to  Van- 
dalia,  and  later  to  Springfield;  that  of  Tennessee  from  Knoxville  to 
Nashville;  and  that  of  Pennsylvania  from  Philadelphia  to  Harrisburg. 
The  centrally  located  capitals  of  Ohio,  Indiana,  Iowa,  Missouri,  and 
South  Dakota  illustrate  the  same  principle.  On  the  other  hand,  where 
the  mass  of  the  population  is  in  one  section  of  the  state,  the  capital 
is  likely  to  be  located  there.  Thus  Boston,  Albany,  Lincoln,  and 
Topeka,  though  far  from  the  geographic  centers  of  their  respective 
states,  are  not  far  from  the  centers  of  population  in  each  case.  The 
question  of  accessibility  was  considered,  among  others,  in  choosing 
the  site  for  the  national  capital,  but  with  the  growth  of  the  West  it 
has  come  to  have  a  marginal  location. 

Health  and  pleasure  resorts.  The  leading  cities  of  this  type 
have  been  stimulated  in  their  growth  by  geographic  conditions  which 
make  them  attractive  to  the  tourist  or  beneficial  to  the  invalid; 
most  of  them  are  ocean,  mountain,  or  mineral  spring  resorts.  The 
attraction  of  the  ocean  resorts  lies  partly  in  their  facilities  for  boat- 
ing and  bathing,  but  chiefly  in  the  occurrence  of  the  cool  sea-breeze 
(p.  74)  in  the  hot  days  of  summer,  and  in  the  tempering  effects  of 
winds  from  the  sea  in  winter.     Newport  and  Atlantic  City  are  exam- 


LOCATION  OF  COLONIAL  CITIES  405 

pies,  Asheville  (North  Carolina)  and  Colorado  Springs  are  among 
the  best-known  mountain  resorts  (pp.  131,317)  of  the  United  States, 
and  Hot  Springs,  Arkansas,  is  the  most  prominent  health  resort 
created  by  "medicinal"  springs  (p.  211).  Los  Angeles  and  several 
neighboring  places  in  southern  California  have  become  important 
resorts  chiefly  for  climatic  reasons. 

Location  of  early  cities.  At  one  time  people  were  gathered 
in  villages  and  cities  chiefly  because  of  the  necessity  for  defense. 
For  this  reason  many  old  cities  are  located  in  places  affording  pro- 
tection, as  on  hiUs  and  islands.  Considerations  of  defense  as  well 
as  of  trade  located  many  of  the  towns  founded  in  this  country  during 
the  colonial  period. 

The  site  of  Boston  was  chosen  because  of  (i)  its  strength  for  defense,  (2)  its 
harbor,  and  (3)  a  supply  of  good  water.  Boston  peninsula  was  connected  with 
the  mainland  by  a  narrow  isthmus,  so  low  that  for  years  it  was  under  water  at  high 
tide  if  a  strong  wind  blew  off  the  bay.  This  favored  defense  toward  the  land.  The 
harbor  is  roomy,  deep,  farther  inland  than  any  other  north  of  Cape  Cod,  and  is 
located  centrally  on  the  coast  of  Massachusetts.  This  favored  trade,  and  helped 
to  make  Boston  the  leading  town  of  the  colony.  New  York  was  founded  on 
Manhattan  Island  for  safety  and  in  the  expectation  that  the  Hudson  River  would, 
as  it  did,  give  it  command  of  the  trade  of  a  large  district.  Quebec  was  founded 
to  guard  the  St.  Lawrence  highway  and  to  command  the  fur  trade  of  the  Interior. 
The  river  is  much  narrower  there  than  at  any  point  farther  downstream  (Why 
advantageous?) ;  the  inland  location  was  expected  to  afford  security  from  European 
enemies;  and  the  "Heights  of  Quebec"  furnished  an  ideal  site  for  a  fortress. 
Montreal  was  laid  out  on  a  hilly  island  in  the  St.  Lawrence  River,  opposite  the 
mouth  of  the  Ottawa  River.  Thus  it  was  reasonably  safe  from  unexpected  attack, 
and  able  to  draw  upon  the  trade  of  both  valleys. 


Questions 

1.  Discuss  the  leading  occupations  of  the  United  States  as  factors  affecting 
density  of  population. 

2.  Why  are  there  more  important  cities  in  the  United  States  on  the  Atlantic 
coast  than  on  the  Pacific  coast? 

3.  Compare  and  contrast  the  commercial  advantages  of  the  seaports  of  south- 
eastern and  northeastern  United  States. 

4.  Why  are  there  fewer  cities  on  the  Great  Lakes  in  Canada  than  in  the  United 
States? 

5.  Give  examples,  not  mentioned  in  the  text,  of  cities  which  have  profited 
from  their  positions  (i)  on  rivers  at  the  head  of  navigation,  (2)  at  the  junctions  of 
important  rivers. 

6.  Lexington  was  for  years  the  largest  community  in  Kentucky.  Now  the  pop- 
ulation of  Louisville  is  more  than  six  times  that  of  Lexington.      Explain  the  change. 


4o6  DISTRIBUTION  OF  POPULATION 

7.  Why  has  Chicago  derived  greater  commercial  advantages  from  its  location 
near  the  head  of  Lake  Michigan,  than  Duluth  has  from  its  position  near  the  head 
of  Lake  Superior? 

8.  Why  are  yio  of  the  cities  in  the  United  States  having  in  1910  a  population 
of  more  than  100,000  situated  east  of  the  Missouri  River  and  north  of  the  Ohio? 

9.  (i)  Explain  the  relatively  small  population  (1900)  of  (a)  southern  Florida 
and  (b)  northern  Wisconsin  and  northern  Michigan,  as  shown  by  Fig.  281. 

(2)  Explain  the  distribution  of  population  in  (a)  Montana,  (b)  the  belt  through 
southeastern  Idaho  and  Utah,  and  (c)  New  JSIexico. 

(3)  Account  for  the  areas  of  relatively  dense  and  of  relatively  sparse  population 
in  California. 

(4)  Cite  illustrations  (not  involved  in  preceding  questions)  from  the  map, 
showing  the  influence  on  the  distribution  of  population  of  (a)  topography,  (b) 
means  of  communication,  and  (c)  natural  resources. 

10.  (i)  Why  is  the  railroad  web  (Fig.  279)  thickest  in  the  northeastern  quarter 
of  the  country? 

(2)  Account  for  the  thinness  of  the  railroad  net  in  northern  New  England, 
northern  New  York,  and  the  northern  Lake  Region. 

(3)  Why  is  the  dominant  direction  of  railroads  east-west  in  the  Great  Plains? 

(4)  Why  the  relatively  small  railroad  mileage  of  the  western  half  of  the  country? 

(5)  Explain  the  distribution  of  railroads  in  California, 


INDEX 


Abrasion  by  sand,  201 

Africa,  area  and  population  in  tem- 
perate zone,  113;  area  and  population 
in  tropics,  98;  general  features  of,  25; 
rivers  of,  25,  269;  trade  with  U.  S., 
140,  141 

Agricultural  implements,  manufacture 
of,  382 

Agriculture,  on  alluvial  fans,  236;  in 
equatorial  forests,  338;  in  irrigated 
lands,  297,  298;  leadership  of  U.  S. 
in,  359;  in  oases,  334;  in  mountains, 
311;  and  rainfall,  59,  76,  80,  119,  128, 
129,  291;  in  semi-arid  regions,  327;  in 
tropical  grass  lands,  104;  in  the 
United  States,  357-370 

Air.     See  Atmosphere 

Alaska,  agriculture  in,  121,  137;  cli- 
mate of,  79,  120,  136;  coast  of,  343; 
fisheries  of,  376;  glaciers  of,  249,  250, 
251 ;  gold  mining  in,  378;  precipitation 
in,  79 

Aleutian  Islands,  194 

Alfalfa,  30,  297,  363 

Alluvial  cones  and  fans,  235,  236 

Alluvial  plains,  237 

Alluvial  terraces,  243 

Alluvium,  165 

Alps  Mountains,  307,  317;  glaciers  of, 
250;  life  on  sunny  vs.  shady  slopes, 
44;  stock-raising  in,  314;  zones  of 
vegetation  in,  313 

Altitude  and  climate,  109,  130 

Altitude  and  pressure,  66,  in 

Altitude  and  temperature,  44,  52,  109, 
130 

Aluminum,  182-183,  377 

Amazon  River,  104,  271,  345,  351 

American  waterways,  271-287;  im- 
provement of,  287 

Andes  Mountains,  307,  320;  as  cHmatic 
barrier,  77,  105,  119  _ 

Animal  life,  of  Antarctic  region,  136;  of 
Arctic  region,  137,  336;  in  caverns, 
212;  in  deserts,  107,  331;  in  the  sea. 


Animal  life  —  continued 

156-158;  and  scil  formation,  164;  in 
tropical  forests,  338.    See  Liji 

Animal  products,  366-370 

Antarctic  circle,  15,  133 

Antarctic  region,  climate  of,  135;  life  of, 
135-136 

Antarctica,  snow  and  ice  of,  251 

Anthracite  coal,  315,  377,  386 

Anticyclones,  83,  85,  89,  90,  93 

Aphelion,  7 

Appalachian  Mountains,  and  early  dis- 
tribution of  population,  392,  394;  and 
early  western  settlements,  274;  forest 
reserve  in,  173,  317;  in  history,  308; 
inhabitants  of  southern,  310;  soils  of, 
173;  structure  of,  305 

Apples,  365 

Arabia,  desert  of,  331,  ^2>z,  334 

Arctic  circle,  15,  133 

Arctic  regions,  climate  of,  136;  ice  of, 
136;  life  in,  137-138,  Z2>^ 

Argentina,  122,  327 

Arid  climate  in  temperate  zones,  123 

Arid  regions  of  the  U.  S.,  79,  126 

Arid  plains,  life  in,  330-336 

Artesian    wells,    209,    302;    in    oases, 

334 

Asia,  area  and  population  in  tropics,  98; 
caravan  trade  in,  335;  cHmatic 
changes  in,  79;  general  features  of,  24; 
monsoons  of,  75,  108-109;  rivers  of, 
269;  trade  with  U.  S.,  140,  141 

Asiatic  cholera,  109 

Asteroids,  4 

Atlantic  City,  404 

Atmosphere,  circulation  of,  72-74;  com- 
position of,  28-29;  density  of,  27; 
functions  of,  27;  heating  of,  39; 
height  of ,  28 ;  impurities  of ,  29,  3 1 , 3 2 ; 
relation  to  rest  of  earth,  27;  tempera- 
ture of,  34;  weight  of,  27,  66;  work  of, 
204 

Atmospheric  pressure,  and  altitude,  66, 
in;  distribution  of,  67 


407 


4o8 


INDEX 


Australia,  area  and  population  in  tem- 
perate zone,  113;  area  and  population 
in  tropics,  98;  climate  of,  105,  106, 
109,  326;  clroughts  in,  80,  130;  general 
features  of,  24;  grazing  in,  327;  Great 
Barrier  Reef  of,  159,  354;  population 
of,  105,  106 

Automobiles,  388 

Bacteria,    of    air,    76;   nitrogen-fixing, 

30 
Baltimore,  131,  286,  385,  401 
Bananas,  339 

Barley,  44,  119,  121,  129,  362 
Barometers,  66 
Barriers,  348 
Bars,  349 
Base-level,  223 
Base-level  plain,  227 
Beach,  348 

Birmingham,  386,  403 
Bituminous  coal  mined  in  U.  S.,  377 
Blizzards,  90 
Block  mountains,  304 
Bolivia,  44,  102,  no,  in,  131,  320 
Boot  and  shoe  industry,  383,  389 
Borax  deposits,  126 
Boston,  344,  376,  401,  404,  405 
Brazil,  53,  104,  271 
Bread  fruit,  339 
Brick,  manufacture  of,  266 
British  Isles,  advantages  of  isolation,  20; 

agriculture  in,  121,  361;  climate  of, 

47,  SI,  120,  123, 150;  fisheries  of,  157; 

rivers  of,  246,  271 
Bubonic  plague,  109 
Buckwheat,  363 
Buffalo,  279,  282,  286,  289,  302,  390, 

402 
Buffaloes,   327,    328;    bones    used   for 

fertilizer,  170 
Building  stones,  175,  377 
Butte.  330,  404 
Butter,  manufacture  of,  380,  386 

Caldera,  195 

California,  climate  of,  77,  79,  I18,  120; 

fruit  of,  53,  119,  297,  379;  gold  in, 

175,  181,378;  oil  in,  179,382 
California  Trail,  309 
Camels,  107,  331,  332 
Campos,  104 
Canada,  15,  47,  90,  129,  130,  137,  140, 

141,  214,  246,  249,  253,  258,  263,  280, 

282,  290,  318,  405 


Canals,  285-287;  in  foreign  countries, 
287;  influence  of,  277,  286;  in  U.  S., 
285-286 

Canning  industries,  379,  386 

Canyons,  230;  and  human  activities, 
228 

Caravans,  331,  334,  335 

Carbon  dioxide,  29,  30-31,  161,  178;  in 
sea-water,  144 

Catskill  Mountains,  306,  311,  317 

Cattle,  366-367 

Caverns,  212 

Cement  produced  in  U.  S.,  176,  377 

Cereals.    See  Corn,  Wheat,  etc. 

Changes  of  level  of  land,  185-187,  2$f^ 

Chemicals  and  allied  products,  384,  388 

Cheese,  manufacture  of,  380,  386 

Chicago,  279,  281,  282,  302,  328,  380, 
383, 385,  386,  389,  397,  402,  403 

Chile,  105,  119,  121 

China,  80,  109,  122,  165,  166,  242,  243, 
269,_  308,  312,  317,  327,  353,  387; 
famines  in,  109;  Great  Wall  of,  327; 
isolated  development  of,  308 

Chinook  winds,  90 

Cincinnati,  276,  302,  389,  402 

Circle  of  illumination,  11,12 

Circulation  of  air,  72-74 

Cities,  air  of,  32;  on  alluvial  terraces, 
243;  commercial,  401;  on  deltas,  243; 
fogs  of,  62;  on  Great  Lakes,  279,  282, 
402;  increasing  number  and  size  of, 
399;  location  of,  3,  399-405;  manu- 
facturing, 403;  about  mines,  315,  403; 
on  rivers,  239,  240,  401,  402;  in 
tropics,  1 10;  types  of,  399 

Civil  War,  Confederate  defenses  along 
Mississippi,  239;  and  Great  Appa- 
lachian Valley,  173;  and  Mississipp? 
delta,  242;  sectionalism  leading  to, 
364;  use  of  wind-gaps  in,  234 

Clays  and  clay  products,  176,  266,  377. 

384, 389 

Cleveland,  279,  282,  302,  383,  386,  390 

Cliff-dwellers,  230 

Cliffs,  347 

Climate;  affected  by  altitude,  77,  79, 
106,  109,  130,  334;  affected  by  ocean 
currents,  150;  and  cereals,  59,  121, 
127-128,  129;  changes  of,  31,  79,  254; 
chief  factors  of,  34;  as  factor  in  life  of 
plains,  323;  and  manufacturing  in- 
dustries, 383 

Climates,  of  polar  regions,  133-139;  of 
temperate  zones,  113-132;  of  tropical 


INDEX 


409 


Climates  —  continued 
regions,  98-112;  of  the  U.  S.,  118, 
120, 125-128,  130 

Cloudiness,  64,  84 

Clouds,  62-64 

Coal,  176-178;  carbon  dioxide  produced 
by  burning  of,  30,  178;  conservation 
of,  177-178;  distribution  of  deposits, 
176-177;  duration  of  supply  in  U.  S., 
177;  and  manufacturing,  381;  mining 
of,  177,  378;  river  trade  in,  278,  279; 
total  amount  in  U.  S.,  177;  trade  on 
Great  Lakes,  282 

Coastal  Plains,  21,  322;  Atlantic,  171, 
302,  324,  392 

Coast-lines,  and  harbors,  341-356;  char- 
acteristics of,  341;  importance  of,  341 

Cod  fisheries,  375 

Coke,  386 

Cold  waves,  90 

Colorado  Canyon,  230 

Colorado  River,  279,  290;  delta  of,  241 

Columbia  River,  279,  287,  376,  397 

Commerce,  of  American  seaports,  352; 
of  the  desert,  334;  difficulties  of,  in 
tropical  countries,  60;  of  the  Great 
Lakes,  279-285;  as  influenced  by 
form  of  the  earth,  6;  of  Mississippi 
System,  274-279;  on  the  ocean,  140, 
141,  341;  and  trade-winds,  107;  of 
tropical  forests,  104,  339;  of  U.  S. 
with  other  countries,  140,  141 

Commercial  cities,  401 

Conduction,  38 

Connecticut  Valley,  influence  on  dis- 
tribution of  population,  172, 220,392; 
mountains  of,  199;  terrace  towns  of, 

243 

Continental  climate,  of  temperate 
zones,  122;  in  U.  S.,  125 

Continental  shelf,  19,  20 

Continents,  comparison  of,  24-25; 
grouping  of,  20;  and  ocean  basins,  19; 
and  oceans,  and  temperature,  50 

Contour  maps,  16-17 

Conservation,  of  coal,  177-178,  289;  of 
forest  resources,  373;  of  ground- 
waters, 210;  of  iron,  180;  of  lead,  182; 
of  mineral  resources,  183;  of  petrole- 
um, 179;  of  soils,  168;  of  waters  in 
irrigation,  294-295 

Convection,  38-39 

Copper,  181,  315;  mines  of  Lake 
Superior  region,  181,  378;  produced  in 
U.  S.,  181.  377 


Coral  reefs,  142,  158- .'59 

Corn,  climate  for,  59,  80,  121,  128; 
distribution  of,  129,  359;  and  frosts, 
53;  production  of,  358,  359;  uses  of, 
360,  368;  water  needed  by,  32,  207 

Corrasion,  217 

Cotton,  170,  171,  325,  363,  358 

Cotton  gin,  364 

Cotton  manufactures,  60,  364,  382,  387 

"Cow  towns,"  328 

Crater  Lake,  195 

Creep,  of  soils,  214 

Crops,  of  chief  importance  in  U.  S.,  358, 
359;  grown  in  mountains,  313;  and 
marine  climate,  121;  and  rainfall,  76, 
80,  119,  128,  129;  and  relative  humid- 
ity, 59;  rotation  of,  169.  Se^ 
Agriculture 

Crustal  movements,  185 

Cumberland- Alleghany  Plateau,  soils  of, 

173 

Cumberland  Gap,  234 

Cumberland  National  Road,  232,  308 

Cycle  of  erosion,  227 

Cyclones,  83,  85;  factors  in  climate,  79, 
85,  123;  height  of,  90;  movements  of, 
85,  89;  places  of  origin,  89;  and 
thunder-storms,  95;  tropical,  91,  106; 
and  weather,  85,  89,  90,  93;  of  winter 
vs.  summer,  89,  90 

Dairy  products,  380,  386 

Danube  River,  270 

Date  palm,  242,  334 

Death  Valley,  58,  126 

Deeps,  143 

Deflection  of  winds,  73,  84 

Degrees,  length  of,  1 1 

Delaware  River,  273,  286,  302 

Delta,  of  Hwang-ho,  242;  of  Mississippi, 
241,  344,  394;  of  Nile,  242 

Deltas,  241-243,  267,  344-345;  and 
commerce,  344-345;  floods  on,  242: 
lakes  on,  243;  soil  of,  242 

Denver,  403,  404 

Deposition,  by  streams,  234-243;  by 
glacial  waters,  266;  by  glaciers,  257- 
261 ;  by  ground- water,  212;  by  waves, 
348;  by  wind,  202 

Deserts,  3,  33o-33(>;  agriculture  in,  332, 
334;  animals  of,  331;  commerce  of, 
334;  life  in,  3,  107,  330-33S;  plants 
of>  65,  330;  political  conditions  in, 
335;  of  snow  and  ice,  136,  336 

Detroit,  302,  389,  390 


4IO 


INDEX 


Dew,  60,  61;  in  tropics,  103 

Diastrophism,  185,  306 

Dikes,  198 

Distributaries,  242,  351 

Distribution  of  population,  392 

Doldrums,  74 

Dover  harbor,  355 

Drainage  basin,  225 

Drift  of  ocean  water,  148 

Drift,  glacial,  165,  257 

Driftless  area,  253 

Droughts,  80,  129;  and  irrigation,  291 

Drowned  valleys  and  harbors,  352 

Drowning  of  streams,  233 

Dry-farming,  65,  173,  329,  399 

Dry  winds,  77 

Dunes,  202,  344,  348,  349 

Dust  of  air,  32,  201 

Earth,  axis  of,  6,  11;  form  of,  5,  11; 
great  relief  features  of,  19;  magnet- 
ism of,  18;  most  favored  of  planets, 
5;  motions  of,  6-8;  orbit  of,  7;  revolu- 
tion of,  6-8;  rotation  of,  6;  size  of.  6 

Earthquakes,  187-191;  causes  of,  188; 
destruction  by,  189;  distribution  of, 
188;  and  movements  of  sea-water, 
148, 191 

Ecuador,  47,  102,  320 

Egypt,  291,333 

Elbe  River,  270 

Electric  Power.  See  Hydro-Electric  Power 

England.  See  British  Isles 

Equator,  6;  days  and  nights  at,  13 

Equatorial  calms,  74,  loi,  102 

Equatorial  climate,  102-104;  and  man, 
3, 103,  104 

Equinoxes,  13 

Erie  Canal,  281,  286,  287,  308,  401 

Erosion,  by  glaciers,  255;  by  ground- 
water, 211,  213;  rate  of,  218,  219; 
stages  of,  225;  by  rivers,  217;  by 
waves,  347;  by  wind,  201 

Eskimos,  137,  138 

Europe,  climate  of  northwestern,  51-52, 
120,  150;  forestry  in,  316-317;  general 
features  of,  24;  glaciation  in,  253; 
rivers  of,  269-271;  trade  with  U.  S., 
140,  141 

Evaporation,  56-57,  58,  64-65 

Fall  Line,  273 

Falls,  230;  and  rapids,  and  cities.  288, 

402 
Farm  animals,  value  of,  369 


Farm  products,  value  of,  358 

Farming.     See  Agriculture 

Faulted  mountains,  304 

Faulting,  188 

Ferries,  and  cities,  403 

Fertilizers,  170,  385 

Figs,  242 

Fiords,  256;  as  harbors,  353 

Fishing  industries,  157,  375-376;  of 
Arctic  peoples,  138,  336;  of  British 
Isles,  157;  conditions  favoring,  157, 
375;  of  Labrador,  129;  of  New  Eng- 
land, 172, 375 

Fissure  eruptions,  197 

Flatboats,  275 

Flax,  364^ 

Flood-plains,  deposits  on,  236;  soils  of, 
241 

Floods,  80,  131,  237,  242,  262 

Flour  and  grist  mill  products,  288,  385 

Fog,  61,  62 

Fogs,  about  icebergs,  149;  in  London, 
32,  62;  over  ocean  currents,  152;  in 
polar  regions,  135 

Food  products,  384,  385;  of  the  sea,  157 

Forecasting  of  weather,  93 

Forest  fires,  373 

Forest  products,  value  of,  371 

Forest  reserves,  165,  173,  299,  316 

Forest  Service,  373,  380 

Forests,  conservation  of,  373;  of  equa- 
torial regions,  103,  337;  evil  effects  of 
removal,  317;  favored  by  humid  cli- 
mate, 121,  123;  and  irrigation,  298; 
in  mountains,  131,  173,  175;  petrified, 
79;  reclamation  of  sand  areas  by,  165, 
204;  reduce  erosion,  169,  222;  repel 
settlers,  397;  of  U.  S.,  370;  and  water 
power,  290 

France,  53,  118,  120,  270,  290, 312, 317, 
352,  361,  373 

Frosts,  53,  54-55,  61,  119,  129 

Fruits,  in  irrigated  lands,  297;  preserv- 
ing of,  379,  386;  production  of,  in 
U.  S.,  365;  production  of ,  near  water 
bodies,  53;  shipment  of  perishable, 
94;  in  sub-tropical  climates,  119 

Fur  trade,  of  Great  Lakes,  280;  in 
mountains,  318 

Furniture,  manufacture  of,  288,  380, 
387 

Galveston,  harbor  of,  354;  sea-wall,  92: 

storm,  91 
Ganges  River,  242,  269,  351 


INDEX 


411 


Geography,  definition  of,  i ;  divisions  of, 
i;  relations  of,  1-3 

Germany,  53,  123,  176,  270,  287,  290, 
312,  314,  316,  361,  373 

Geysers,  210 

Glacial  deposits,  257;  and  stream 
courses,  264 

Glacial  erosion,  255 

Glacial  period,  252 

Glacial  soils,  165,  172,  173,  174,  175, 
265 

Glacial  waters,  deposits  by,  266;  de- 
posits of,  and  early  settlements  in 
New  England,  172 

Glaciers,  247-267;  effect  on  shore-lines, 
256,  261,  344;  functions  of,  248; 
movement  of,  250;  types  of,  249 

Glass,  389,  390 

Glucose,  360 

Gold,  181,  377,  378;  in  Black  Hills,  397; 
in  California,  175,  181,  397;  produc- 
tion in  U.  S.,  377 

Grand  Canyon  of  the  Colorado,  228 

Granite,  175,  302,  380 

Grazing,  173, _  175,  385,  397;  in  arid 
U.  S.,  175;  in  the  Great  Plains,  127, 
173;  328,  366;  on  margins  of  deserts, 
332;  in  mountains,  314;  in  public 
domain,  314;  in  semi-arid  plains,  326, 
327,  328,  329 

Great  Britain.     See  British  Isles 

Great  Lakes,  cities  on  shores  of,  279, 
282,  402;  commerce  of,  279-285;  coal 
trade  of,  282;  development  of  steam 
navigation  on,  281;  early  navigation 
of,  280;  freight  rates  on,  268;  grain 
trade  of,  284;  history  of,  264;  iron  ore 
trade  of,  282;  lumber  trade  of,  283; 
navigation  season  on,  246;  steel 
freighters  on,  284;  total  shipments  on, 
280 

Great  Plains,  future  use  of,  329,  366; 
history  of,  327;  sand  dunes  of,  165; 
soils  of,  173;  underground  waters  of, 
210,  302 

Greenland,  glaciers  of,  250;  settlements 
in,  137;  temperatures  in,  136 

Ground-water,  205-215;  amount  of, 
205;  conservation  of,  210;  courses 
followed  by,  206;  importance  of,  207; 
movement  of,  206;  surface,  205;  work 
of,  211 

Guano,  121,  170 

Gulf  of  Mexico,  85,  355 

Gulf  Stream,  149,  152 


Gullies,  destroy  land,  221;  growth  of,  220 
Gypsum,  176,  377 

Hail,  95 

Hammerfest,  climate  of,  134;  harbor  of, 
152 

Hanging  valleys,  256 

Harbors,  350-355;  conditions  deter- 
mining value  of,  350-351,  401;  on 
Great  Lakes,  279;  and  ice,  247;  im- 
provement of,  354;  in  rivers,  351, 
352;  and  tides,  152,  156 

Hawaiian  Islands,  105,  194 

Hay,  297,  363 

Health  resorts,  44,  118,  131,  317,  404 

Heat  of  atmosphere,  34,  39;  distributed 
by  wind,  51;  measurement  of,  34-35 

Hemp,  364 

High-pressure  belts,  69,  72,  73 

Himalaya  Mountains,  19,  44,  79,  311 

Holland,  301 

Horses,  368,  369 

Hot  waves,  90 

Hot  winds,  65 

Hudson  River,  153,  272,  302 

Hudson  Valley,  early  population  of,  392; 
and  growth  of  New  York  City,  401 

Humid  climate  in  temperate  zone,  123, 
127,  129 

Humid  plains  of  low  latitudes,  337 

Humid  regions  of  U.  S.,  127 

Humidity,  59;  and  air  pressures,  72; 
and  crops,  59 

Humus,  160,  373 

Hurricanes,  91-92,  106 

Hwang-ho  River,  165,  242,  269 

Hydro-electric  power,  231,  288,  289, 
382 

Ice,  of  polar  regions,  135,  136;  on  rivers, 
246;  on  seas  and  lakes,  246;  work  of, 
246 

Icebergs,  251;  dangerous  to  steamships, 
149 

Igneous  rocks,  315 

Imperial  Valley,  242 

India,  famines  in,  80,  109;  irrigation  in, 
291;  lava  fields  of,  198;  monsoons  of, 
75,  108;  population  of,  109,  311;  rain- 
fall in,  108;  rivers  of,  269 

Indians,  check  expansion  of  whites, 
394;  of  Great  Plains,  327,  328;  of 
southern  Appalachians,  3 1 1 ;  of  South- 
west, 3S3 

Indus  River,  269 


412 


INDEX 


Industries,  location  of,  379-383;  of  the 

U.S.,  357-391 

Inland  waters  and  their  uses,  268-303 

Insolation,  35-37 

Intermediate  zones.  See  Temperate 
Zones 

Iron,  179-180;  conservation  of ,  180;  dis- 
tribution of  deposits,  180;  estimated 
supply  in  U.  S.,  179,  377;  in  rocks  and 
soils,  162 

Iron  and  steel  industries,  282,  384,  386 

Iron  ore,  importance  of  location,  378; 
of  Lake  Superior  region,  180,  282, 
315,  380,  386;  movement  of,  282; 
production  of,  in  U.  S.,  179,  180 

Irrigable  land,  area  of,  293 

Irrigated  land,  crops  of,  297;  popula- 
tion capacity  of,  297;  value  of,  292 

Irrigation,  126,  173,  175,  291-298,  329, 
397;  from  artesian  wells,  210;  early 
practice  of,  in  West,  291;  in  Egypt, 
291;  government  projects,  295;  in 
humid  states,  298;  in  India,  269,  291; 
and  National  Forests,  298;  in  semi- 
arid  belt  of  U.  S.,  173;  in  sub-tropical 
regions,  119;  in  tropical  regions,  104, 
no 

Islands,  from  coral  reefs,  158;  leading 
types  of,  in  ocean,  20;  off  glaciated 
coasts,  256,  261;  of  volcanic  origin, 

194. 
Isobaric  maps,  68,  70,  71 
Isobars,  67,  83;  courses  of,  69-72 
Isothermal  maps,  46,  48,  49 
Isotherms,  45,  84;  courses  of,  50-52 
Italy,  53,  118,  166,  196,  253,  290,  312, 

345 

Japan,  188, 312, 316, 387 

Japan  Current,  150,  152 

Java,  98,  99,  102 

Jetties  of  the  Mississippi,  217,  352 

Kaffir  corn,  173,  363, 

Kansas  City,  277,  302,  328,  380,  385, 

402 
Kaskaskia,  240,  404 
Krakatoa,  196,  201 

Labrador,  128,  129 
Labrador  Current,  150 
Laccoliths,  198,  305 
Lagoons,  348;  as  harbors,  348,  353 
Lake  Agassiz,  262;  settlement  of  floor 
of,  263 


Lake  Bonneville,  186 

Lake-breezes,  74 

Lakes,  on  deltas,  243;  glacial,  255,  261; 
oxbow,  239;  as  resorts,  264;  as 
sources  of  water  supply,  302 

Land  reduction,  rate  of,  218,  219 

Land-breezes,  74 

Lands,  area  and  height  of,  19,  20;  best 
uses  of,  in  North  America,  174 

Landslides,  189,  214;  and  movements  of 
sea-water,  148 

Latitude,  9;  and  isotherms,  50 

Lava,  192;  intrusions  of,  198 

Lava  fields,  of  India,  198;  of  the  North- 
west, 197 

Lead,  182,  397;  production  in  U.  S., 
182, 377 

Leadville,  Colo.,  315,  381,  397 

Leather  and  its  products,  384,  389 

Lemons,  119,  297 

Life,  in  Antarctic  regions,  135-136;  in 
Arctic  regions,  137,  336;  in  arid 
plains,  330;  in  deserts,  3,  107,  330- 
335;  in  the  Great  Plains,  327;  in 
humid  plains  of  low  latitudes,  337; 
in  mountains,  309-318;  in  oases,  334; 
in  plains,  324-340;  in  plateaus,  320; 
in  the  sea,  156-158;  in  semi-arid 
plains,  326;  in  the  temperate  zones, 
116,  i2'i,  126,  127,  128,  129;  in  trade- 
wind  belts,  107;  in  the  tropical  zone, 
100,  loi,  103,  104,  107;  in  well- 
watered  plains  of  middle  latitudes,  3  24 

Lightning,  95 

Limestone,  175;  soils  from,  164,  171,  173 

Liquors  and  beverages,  3S4,  389 

Littoral  currents,  346 

Llanos,  104 

Load  of  streams,  166,  217 

Loess,  165,  173 

London,  air  of,  32,  62;  commerce  helped 
by  tides,  271;  fogs  of,  32,  62;  harbor 
of,  352 

Longitude,  9;  and  time,  10 

Los  Angeles,  302,  405 

Louisville,  275,  277,  402;  tornado,  97 

Lumber  and  its  manufactures,  384,  387 

Lumber  trade,  of  the  Lakes,  283;  of 
Mississippi  System,  278 

Lumbering,  76,  316,  370-373;  kinds  of 
wood  cut,  371;  in  Lake  states,  283, 
372;  in  mountains,  316;  by  states,  372 

Macaroni,  128 
Magnetism  of  earth,  18 


INDEX 


413 


Malaria,  in  tropics,  103;  in  U.  S.,  128, 
301 

Malaspina  Glacier,  251 

Manchester  Ship  Canal,  287 

Mantle  rock,  160 

Manufacturing  cities,  383,  403;  of  New 
England,  288,  381 

Manufacturing  industries,  378-391;  of 
desert  people,  333;  factors  controlling 
location  of,  379;  groups  of,  384;  of 
interior  river  cities,  276-277;  of 
mountaineers,  309,  318;'  total  value 
of  products  in  U.  S.,  378,  379 

Map  projections,  15 

Marble,  176,  380 

Marshes,  and  flow  of  streams,  262; 
glacial,  173,  260;  reclamation  of,  171, 
241,  242,  300 

Marine  climate,  in  high  latitudes,  iig; 
and  crops,  121 

Marl,  171,  262 

Mature  topography,  226 

Mean  annual  temperature,  35 

Meanders  of  streams,  239 

Meat-packing  industry,  328,  380,  385 

Mediterranean  climate,  118 

Mercator's  projection,  16 

Meridians,  8,  9 

Metal  products,  181-182,  381,  384,  388 

Meteors,    28 

Mexico,  22,  44,  240,  320;  trade  with 
U.  S.,  140,  141 

Milch  cows,  366,  367 

Millet,  363 

Milwaukee,  282,  302,  389 

Mineral  fuels,  176 

Mineral  industries,  distribution  of,  377 

Mineral  plant  foods,  169 

Mineral  products,  175;  substitution  for 
wood,  176;  of  U.  S.,  377 

Mineral  resources,  conservation  of,  183 

Mineral  springs  and  waters,  211,  377 

Mining,  126,  311,  330,  376-378;  in- 
fluence on  distribution  of  people  and 
growth  of  cities,  315,  330,  397,  403; 
in  mountains,  315 

Minneapolis,  288,  302,  386 

Missouri  River,  240,  274,  277.  302; 
influence  on  distribution  of  popula- 
tion, 394;  transportation  of  sediment 
by,  1,67  _ 

Mississippi  River,  240,  243,  246,  273- 
279,  286,  290,  302,  352;  as  a  bound- 
ary, 274;  delta  of,  241,  242;  influence 
on  distribution  of  population,   274, 


Mississippi  River — continued 

394;  traffic  on,  279;  transportation  of 

sediment  by,  166,  217 
Mohawk  Valley,  272;  early  population 

of,  392 
Moisture  of  atmosphere,  56-65 
Monadnocks,  227 
Monsoons,  75,  108-109;  and  trade  on 

Indian  Ocean,  75 
Monsoon  climate,  108-109 
Monsoon  rains,  79,  108,  109 
Montreal,  401,  405 
Moon,  4,  5;  and  tides,  147,  154-156 
Moraines,  258;  use  of  hilly,  173,  259 
Mosquitoes,  103,  301 
Mt.  Everest,  19 
Mountain  climate,  in  middle  latitudes, 

130;  in  the  tropics,  1 09-1 11 
Mountaineers,  industries  of,  318;  life  of, 

309 
Mountains,  22,  304-319;  agriculture  in, 
311;  as  barriers,  307,  311;  destruction 
of,  306;  distribution  of,  23,  304;  effect 
on  precipitation,  77,  79, 106,  131,334; 
as  forest  reserves,  316;  life  in,  309- 
318;  mining  in,  315;  passes  in,  232, 
234,  308,  403;  as  resorts,  i^i,  317, 
404;  settlement  of,  311;  stock-raising 
in,  314;  summer  capitals  in,  44; 
sunny  vs.  shady  slopes,  44;  types 
of,  304;  zones  of  vegetation  in,  no, 

Narrows,  232 

Nashville,  277,  402,  404 

National  Forests,  165,  173,  299,  317; 
grazing  in,  315;  lumbering  in,  373;  to 
reclaim  sandy  areas,  165 

National  Monuments,  317 

National  Parks,  249,  317,  318 

Natural  gas,  179;  and  location  of 
industries,  381,  390;  produced  in 
U.  S.,  377;  waste  of,  29,  179 

Natural  levees,  237;  and  early  popula- 
tion of  Louisiana,  237 

Naval  stores,  325,  380 

Navigable  streams  of  U.  S.,  271 

Navigation,  231,  268-287;  affected  by 
tides,  152;  on  canals,  285-287;  cities 
on  rivers  at  head  of,  401;  of  Great 
Lakes,  279-285;  improvement  of, 
287;  of  rivers,  268-279 

Neap  tides,  156 

New  England,  early  industries  in,  172, 
383,  388;  early  population  of,  392; 


414 


INDEX 


New  England  —  continued 

fisheries  of,  158,  375;  manufacture  of 
cotton  in,  364,  382;  manufacturing 
cities  of,  288,  381;  mountain  resorts 
in,  317;  rivers  of,  272;  soils  of,  172; 
use  of  water  power  in,  288 

New  Orleans,  217,  242,  243,  275,  277, 

351 

New  York,  380,  382,  383,  397,  403; 
commercial  leadership  of,  277,  351, 
401;  and  Erie  Canal,  286;  harbor  at, 
35°,  352,  354;  location  of,  405;  water 
supply  of,  302 

Niagara  Falls,  289 

Nile  River,  268,  269;  delta  of,  242 

Nitrate  deposits,  121 

Nitrogen,  28,  29-30;  in  sea-water,  144; 
compounds  in  soil,  29,  170 

Nomads,  104,  326,  332,  3S3 

North  America,  area  and  population  in 
tropics,  98;  best  use  of  lands  of,  174; 
commerce  of,  140,  141;  general  fea- 
tures of,  25;  glaciation  of,  252 

Northers,  90 

Norway,  51,  121,  134,  137,  256,  314, 
341 

Oases,  334 

Oats,  128,  129,  362;  climate  for,  121, 
362;  distribution  of,  129,  362 

Ocean  areas,  20,  98,  113,  142 

Ocean  basins,  19;  and  continents,  19- 
20 

Ocean  currents,  145,  148-152;  and  cli- 
mate, 51,  150;  cold,  i4j,  150;  equa- 
torial, 149,  150;  and  isotherms,  51; 
map  of,  151;  warm,  145,  150 

Oceans,  140-159;  area  of,  20,  142;  chief 
source  of  water  vapor,  57;  depth  of, 
19,  143;  distribution  of,  98,  99,  113, 
114,  115,  141;  exploration  of,  142; 
ice  on,  246;  importance  of,  140;  land 
areas  tributary  to  several,  23 ;  life  of, 
156-158;  materials  of  bottom,  142; 
topography  of  bottom,  143;  trade  on, 

341 
^hio  River,  220,  274,  302 
Oil.     See  Petroleum 
Old  topography,  226,  227 
Olives,  119 

Omaha,  302,  328,  380,  385 
Oozes,  142 
Oranges,  119,  297 
Oregon  Trail,  220,  309 
Ores,  212,  315;  mined  in  U.  S.,  377 


Outwash  plain,  266 

Oxygen,  of  the  air,  29,  30,  i0i;  in  sea- 
water,  144,  156;  in  soils,  169,  170 
Oyster  fisheries,  376 
Ozone,  29 

Packing  industry,  328,  380,  385 
Palestine,  2,  x66 
Panama  Canal,  191,  287,  355 
Paper  and  printing,  384,  388 
Parallels,  8 

Pastoral  tribes,  104,  326,  327,  332 
Pelee,  192,  197 
Peneplains,  227 
Penguins,  136 
Peoria,  277,  389 
Perihelion,  7 
Peru,  77,  no,  121 
Petrified  wood,  213 

Petroleum,  178-179;  and  manufac- 
turing, 382;  produced  in  U.  S.,  179, 

377 
Philadelphia,  273,  286,  302,  352,  355, 

382,  383,  385,  386,  401,  403,  404 
Philippines,  44 
Phosphates,  1 70-1 71;  produced  in  U. 

S.,  377 

Piedmont  alluvial  plain,  236 

Piedmont  glaciers,  249,  251 

Piedmont  Plateau,  21;  early  population 
of,  392;  soils  of,  173 

Pig  iron  produced  in  U.  S.,  377 

Piracy  of  streams,  233 

Pittsburgh,  275,  276,  C78,  386,  401 

Plains,  21,  322-340;  advantages  of,  322; 
classes  of,  322;  contrasts  among,  21, 
323;  density  of  population  in,  323; 
life  of,  324-340 

Planets,  4,  5 

Plant  life,  of  Antarctic  regions,  135; 
of  Arctic  regions,  137,  336;  de- 
pendence on  ground-water,  207;  in 
deserts,  65,  107,  330;  on  mountain 
slopes,  107,  no,  313;  in  the  sea,  156- 
158;  and  soil  formation,  164;  in  the 
temperate  zones,  119,  121,  12&,  127 
128,  129,  131;  in  the  tropical  zone, 
100,  loi,  103,  104,  107,  no;  and 
water  vapor  of  air,  57 

Plateaus,  21,  no,  319-320 

Pleasure  resorts,  131,  317,  404 

Polar  circles,  15 

Polar  regions,  climate  of,  37,  133-138'. 
extent  of,  133 

Poles,  6;  magnetic.  18;  seasons  at,  14 


INDEX 


41S 


Polyps,  157,  158 

Pompeii,  196 

Population,  center  of,  in  census  years, 
394;  distribution  of,  208,  392-399; 
engaged  in  agriculture,  357;  factors 
aflfecting  density,  392;  maps,  264, 
281,  393,  395,  398,  400;  and  rainfall, 
76,  399;  rural  vs.  urban,  383,  399;  of 
the  tropics,  98,  no;  at  various  alti- 
tudes, no,  399 

Pork-packing,  385 

Portland  cement,  176,  262 

Porto  Rico,  92 

Potassium,  in  soil,  169,  170 

Potatoes,  no,  121,  365 

Pottery,  manufacture  of,  by  Indians, 

333 

Poultry  and  eggs,  370 

Prairies,  settlement  of,  173,  284,  394; 
soils  of,   173 

Precipitation,  64,  76;  and  altitude,  77, 
90,  106,  131,  334;  average  on  lands, 
57;  in  California,  77,  79;  and  density 
of  population,  399;  factors  determin- 
ing, 76;  and  evaporation,  64;  on 
mountains,  77,  79,  131;  in  polar 
regions,  135;  in  trade-wind  zones,  77, 
105;  in  U.  S.,  77-79,  124;  for  the 
world,  78;  in  zones  of  westerlies,  77 

Pressure  of  air,  66;  and  altitude,  66; 
distribution  of,  67;  effects  on  man, 
in;  representation  of,  on  maps,  67 

Pygmies,  339 

Pyrenees,  307;  people  of  western  val- 
leys, 311 

Quarrying,  376 
Quebec,  405 

Radiation,  38 

Railroads,  accidents  on,  and  fogs,  62; 
and  cattle  industry,  328;  competition 
with  waterways,  268,  278;  develop- 
ment of,  397;  freight  rates,  268;  and 
growth  of  cities,  402-403;  problems 
of,  in  equatorial  regions,  104;  pro- 
jected across  Sahara,  335;  routes  of, 
in  rugged  regions,  228,  309;  and 
snowslides,  131;  and  standard  time, 
11;  trans-Appalachian,  308;  of  the 
U.  S.,  396 

Rain,  64;  how  disposed  of,  205 

Rainbow,  95 

Rainfall,  affected  by  altitude,  77,  90, 
106,  131,  334;  and  agriculture,  59,  76, 


Rainfall  —  continued 

80,  119,  128,  129,  291;  annual,  of 
world,  78;  in  the  desert,  106, 108, 334; 
distribution  of,  77-79;  of  marine 
chmates,  120;  of  the  Mississippi 
Basin,  79,  85;  in  polar  regions,  135; 
and  thunder-storms,  95;  in  trade- 
wind  belts,  77,  105;  in  tropical  zone, 
loi,  102,  105,  106,  108;  of  the  U.  S., 
77-79,85.  124;  variation  in,  79;  and 
winds,  76,  85;  in  zones  of  westerly 
winds,  77 

Rapids,  230 

Reclamation,  of  arid  lands,  291-298; 
of  lake  lands,  262,  297,  301;  of  swamp 
lands,  300-301 

Reclamation  Service,  298 

Red  clay,  142 

Reefs,  348;  coral,  158 

Refrigerator  cars,  365,  379 

Reindeer,  336 

Rejuvenation  of  streams,  233 

Relief  features,  19 

Relief  maps,  15 

Rhine  River,  270;  valley,  270,  309 

Rhone  River,  270,  352;  valley,  309 

Rice,  no,  172,  339,  363 

River  navigation,  268-279;  dechne  of, 
278;  development  of,  268,  275; 
present  traffic,  278 

River  system,  225 

River  valleys  and  human  life,  219 

Rivers,  as  boundaries,  240,  274;  com- 
mercial cities  on,  239,  401,  402; 
effect  of,  on  salinity  of  sea-water,  145; 
effect  of,  on  temperature  of  sea-water, 
146;  of  foreign  countries,  269-271; 
ice  of,  246;  and  shore-lines,  344;  tides 
in,  153;  of  U.  S.,  271-279;  work  of, 

215-245 

Rock  waste,  160 

Rocky  Mountains,  as  barriers,  309; 
early  settlements  in,  397;  fur  trade 
in,  318;  and  precipitation,  79;  soils  in, 

174 
Russia,  2,  122,  123,  130,  246,  269,  323, 

327,  365 
Rye,  44,  59,  121,  129,363 

Sahara,  59,  77,  106,  107,  202,  s33,  334, 

335 
St.  Louis,  47,  277,  302,  318,  328,  383, 

389,  402;  tornado  at,  97 
St.  Pierre,  197 
Salmon  industry,  376 


4i6 


INDEX 


Salt,  144,  183;  deposits  of,  126,  144, 
183;  and  early  settlement  of  Interior, 
183,  394;  produced  in  U.  S.,  377;  of 
sea,  144,  212 

San  Francisco,  47,  352,  401;  earthquake 
at,  188,  189 

Sand,  abrasion  by,  201;  deposits  of,  165, 
202;  for  making  glass,  390;  as  water 
carrier,  302 

Sand  bars,  and  navigation,  237 

Sandstone,  176;  soils  from,  164,  171; 
as  water  bearer,  302 

Satellites,  4 

Saturation  of  air,  58 

Sea.     See  Oceans. 

Sea-breezes,  74 

Sea-island  cotton,  363 

Sea-level,  changes  of,  185,  186 

Sea-water,  composition  of,  144;  gases 
in,  144;  movements  of,  145,  146, 
147-156,  1 97;  temperature  of,  145, 146 

Seal  fisheries,  137,  158,  376 

Seasons,  12-15,  36-37,  41-43;  in  high 
latitudes,  43;  in  low  latitudes,  42, 
loi,  102;  in  middle  latitudes,  41,  116 

Sediment,  amount  carried  to  sea,  212, 
217;  how  carried,  216;  of  the  sea- 
bottom,  142 

Semi-arid  climate  in  temperate  zone, 
123, 126 

Semi-arid  regions,  126,  173,  326;  life  in, 
127, 326-329 

Sensible  temperature,  58,  100 

Shackleton  expedition,  135 

Shale,  soils  from,  164;  as  water  bearer, 
302 

Sheep,  368 

Shipbuilding,  172,  384,  390 

Shooting  stars,  28 

Shore  currents,  148 

Shore-hnes,  and  harbors,  341-356;  mod- 
ification of,  343 

Siberia,  47,  123, 134,  136,  137,  246 

Sierra  Nevada  Mountains,  climatic 
barriers,  77,  120,  311 

Silk  manufacture,  381,  387 

Sills,  198 

Silver,  181,  388,  397;  production  in  U. 

S.,  377 
Simoons,  201 
Sirocco,  90 
Slates,  176 
Slavery,  in  Alabama,  325;  and  cotton 

culture,   171,  325,  364;   favored  by 

climate  of  South,  2,  171 


Slumping,  213 

Smelting  industry,  182,  381 

Snoqualmie  Falls,  289 

Snow,  246;  fields,  45,  135,  247;  and 
temperature  of  air,  45;  value  of,  54, 
76,  no 

Snowfall  and  altitude,  131 

Snowshdes,  damage  by,  131 

Soil,  160,  161-171;  alkaUne,  126,  293;  of 
arid  regions,  126,  293;  classes  of,  164; 
conservation  of,  168;  enrichment  of, 
170;  evils  resulting  from  erosion  of, 
167;  factors  determining  f ertihty ,  171; 
and  frost,  53;  human  responses  to, 
324;  importance  to  man,  161;  making 
of,  161-164;  plant  foods  in,  169-171; 
prevention  of  erosion  of,  168;  pro- 
duced from  volcanic  materials,  193; 
provinces  in  U.  S.,  171-175;  of  re- 
claimed swamps,  300;  removal  of, 
166-169;  waste  of,  167 

Solar  system,  4 

Solstices,  7,  13,  36,  41 

'•Soo  Canal,"  282 

South  America,  area  and  population  in 
temperate  zone,  113;  area  and  popula- 
tion in  tropics,  98;  distribution  of 
population  in,  in;  general  features 
of,  25;  rivers  of,  271;  trade  with  U.  S., 
140, 141 

South  Pass,  309 

Spain,  307 

Spanish  Trail,  228 

Spits,  349 

Spring  tides,  15s 

Springs,  208,  301 

£t.  Anthony's  Falls,  288 

Standard  time,  11 

Steamboat  trade  on  Mississippi,  centers 
of,  276 

Steamboats,  275,  281,  284,  341;  losses 
of,  237 

Steamship  routes,  vary  with  seasons, 149 

Steamships,  lost  at  sea,  62,  94,  149 

Stock-raising,  in  mountains,  314;  in  the 
early  western  settlements,  274;  on 
the  Great  Plains,  327,  328,  329 

Storms,  81,  83;  destruction  by,  91-92, 

96,  97 
Streams,  accidents  to,  233;  as  boun- 
daries, 240,  274;  deposition  by,  234; 
and  distribution  of  population,  394; 
importance  of,  in  history  of  U.  S.. 
273;  meanders  of,  239;  as  sources  of 
water  supply,  302;  work  of,  215-245 


INDEX 


417 


Submerged  valleys,  143 

Subsoil,  160 

Sub-tropical  climates,  117;  crops  of,  119 

Sudan, 104,  107,  333 

Suez  Canal,  282,  355 

Sugar,  366,  382 

Sugar-beet,  297,  366 

Sugar-cane,  no,  366 

Sun,  apparent  motion  of,  14;  heat  of, 

as  source  of  power,  106;  nature  of,  4; 

source   of   heat   of  atmosphere,   34; 

and  tides,  147,  155-156;  worship  of, 

108 
Sunshine,  and  cloudiness,  64 
Simstrokes,  58,  90,  100 
Swamps,  reclamation  of,  171,  241,  300- 

301 
Swine,  368,  369 
Switzerland,  44,  249,  250,  290,  310,  311, 

312,314,  316 

Talus,  163 

Tanning  industry,  389 

Temperate  zone,  northern,  seasons  in, 
116,  122;  temperature  range  in,  116, 
122 

Temperate  zones,  area  of  land  in,  113; 
chmate  of,  113-1^2;  extent  of,  113; 
population  of,  113.  114 

Temperature,  and  air  pressure,  67;  and 
altitude,  44;  changes  and  rock-spht- 
ting,  162,  163;  daily  range  of,  52; 
distribution  of,  37-40;  effect  of  snow 
on,  45,  54i  76;  and  evaporation,  58; 
of  land  and  water,  40,  50;  maximum, 
35;  minimum,  35;  modified  by  ocean 
currents,  1 5o;inpolarregions,  133, 135, 
136;  range  of,  47,  52,  54;  representa- 
tion of,  on  maps,  45;  of  the  sea,  145; 
seasonal  range  of,  54;  in  temperate 
zones,  115,  118,  120,  122, 125, 130; in 
tropical  zone,  99-100,  102,  103,  105 

Terraces,  alluvial,  243;  of  drift,  266; 
wave-cut,  347 

Terracing,  for  agriculture,  168,  312 

Textile  manufactures,  60,  384,  387 

Thermometers,  34-35 

Thunder-storms,  95,  102 

Tidal  water  power,  156 

Tides,  148,  152-156,  271 

Till,  257  _ 

Timber-line,  131,  313 

Tobacco,  170,  172,  365 

Tobacco  products,  384,  390 

Tornadoes,  83,  96 


Trade-wind  climate,  77,  105-108;  and 
life,  107 

Trade-winds  and  commerce,  107 

Tree-line,  313 

Tropical  climate,  98-1 1 2 ;  characteristics 
of,  98;  and  disease,  103,  104;  and  Hfe, 
100,  loi,  103,  104,  107;  types  of,  loi 

Troj-ical  forests,  animals  of,  338;  com- 
merce of,  104,  339;  life  in,  3377339 

Tropical  regions,  area  of  land  in,  98; 
climate  of,  98-112;  extent  of,  98; 
future  of,  112;  natives  of,  3, 100,  103, 
104,  107,  no,  II 1, 337;  population  of, 
98,  no 

Tropics  of  Cancer  and  Capricorn,  15 

Truckee  Pass,  309 

Tundras,  336 

Turpentine,  325,  380 

Typhoid  fever,  207 

Undertow,  148 

United  States,  cities  of,  399-405; 
climates  of,  118,  120,  125-128,  130; 
distribution  of  population  in,  392- 
399;  effects  of  glaciation  in,  258-266; 
exports  from,  140;  imports  to,  141; 
irrigation  in,  291-298;  railroads  of, 
396;  rainfall  of,  124;  soils  in  provinces 
of,  1 71-175;  water  power  in,  288- 
290;  waterways  of,  271-287;  wet 
lands  of,  300-301 

Valley  system,  225 

Valley  trains,  266 

Valleys,  as  centers  of  human  activity, 
219;  changed  by  glaciers,  255;  growth 
of,  220-224;  stages  in  history  of,  225 

Vegetables,  297,  365;  canning  of,  379, 

386  .         .  , 

Vegetation,  of  Antarctic  region,  135;  of 
Arctic  region,  43,  137,  336;  in  deserts, 
65,  107,  330;  on  mountain  slopes,  107, 
no,  313;  of  oases,  334;  in  the  tropics, 
100,  loi,  103,  104,  107,  no.  See 
Plant  Life 

Vehicles,   manufacture   of,   384,   388 

Veins,  212,  315 

Venezuela,  104 

Vesuvius,  196 

Volcanic  cones,  20,  143,  193-195,  305; 
destruction  of,  194 

Volcanoes,  191-197;  destructiveness  of, 
196;  distribution  of,  193;  number  of, 
193;  products  of,  192;  in  sea,  20,  143, 
148,  193 


4i8 


INDEX 


Volga  River,  270 

Vulcanism,  191-199;  causes  of,  199 

War  of  1812,  242,  272,  286 

Washington,  D.  C.,  404 

Water  power,  288-290;  afforded  by 
hanging  valleys,  256;  amount  devel- 
oped, 288;  distribution  in  U.  S.,  289- 
290;  furnished  by  mountain  streams, 
121,  248,  256,  319;  furnished  by  tides, 
156;  future  importance,  289;  and 
manufacturing,  288,  381;  in  other 
countries,  290;  of  Ottawa  Valley,  281 

Water  supply,  207,  301-303 

Water  table,  205 

Water-gaps,  232 

Water  vapor,  29,  31-32,  161;  and  air 
pressure,  67,  72;  circulation  of,  57; 
functions  of,  56;  sources  of,  56-57 

Wave-cut  terraces,  347 

Waves  and  wave  action,  148,  345,  347, 
348 

Weather  Bureau,  53,  75,  81;  value  of 
work  of,  53,  94 

Weather  forecasting,  81,  93 

Weather  maps,  81,  82,  86,  87,  88; 
interpretation  of,  83 

Weathering,  161 

Wei's,  artesian,  209;  and  domestic  water 
supply,  210,  302;  and  irrigation,  210; 
pollution  of  waters  of,  207 


West  Indies,  cyclones  of,  91,  92 
Westerly  winds,  rainfall  in  zones  of,  77 
Whaling  industry,  107,  137,  158,  376 
Wheat,   no,   119,   127,   129,  360-362; 
climate  for,  59,  121,  128;  distribution 
of,  128,  129,  361;  production  of,  361 
Whiskey,  360,  389 
Wills  Creek,  narrows  of,  232,  403 
Wind,  72;  velocity  of,  75,  84,  87;  work 

of,  201-205 
Wind-zones,  73-74 
Wind-gaps,  234 

Winds,  72-76;  causes  of,  72,  74;  deflec- 
tion of,  73,  84;  and  distribution  of 
temperature,   51;   easterly,   74;   and 
evaporation,  58;  hot,  65;  importance 
of,  72;  and  movements  of  sea-water, 
147;  periodic,  74;  planetary,  74;  pre- 
vailing,   74;    and    rainfall,    76,    77; 
trades,  74,  loi,  105;  westerlies,  73 
Wine,  manufacture  of,  370,  389 
Wood-pulp,  288,  380 
Wood-working  industries,  380 
Wool  clip  of  U.  S.,  368 
Woolen  manufactures,  381,  387 

Yang-tze  River,  269 
Yellow  fever,  103,  128 
Youthful  topography,  226 

Zinc,  182;  produced  in  U.  S.,  182.  377 


REFERENCE   BOOKS 

The  following  list  contains  some  sixty  books  on  geography  and  related  subjects 
which  might  well  be  in  a  high  school  library.  If  a  reference  library  of  twenty- 
five  books  were  to  be  chosen  from  the  list,  those  which  are  starred  would  be  sug- 
gested as  most  suitable.  If  only  ten  books  were  to  be  chosen,  those  marked  with 
two  stars  would  be  suggested. 

Black  WELDER  AND  Barrows:  Elements  of  Geology.    New  York:  American  Book 
Co.,  1911.     Price,  $1.40. 

Presents  briefly  the  fundamental  principles  of  geology;  helpful  in  answer- 
ing questions  involving  the  relations  of  physiographj'  and  geology. 
Brigham:  Commercial  Geography.    Boston:  Ginn  and  Co.,  1911.     Price,  $1.35. 

Discusses  at  length  wheat,  cotton,  cattle  industries,  iron,  and  coal,  deducing 
from  these  the  principles  of  commercial  geography.     Of  commercial  nations 
the  United  States  is  treated  most  fully.     Many  good  maps  and  diagrams. 
Brigham:    Geographic  Influences  in  American  History.    Boston:    Ginn  and  Co., 
1903.     Price,  $1.25. 

Traces  in  a  suggestive  way  the  effects  of  the  larger  geographic  features 
of  the  United  States  on  many  leading  events  in  its  history. 
**Chisholm:  Handbook  of  Comviercial  Geography.    New  York:  Longmans,  Green 
and  Co.,  1912.     (Revised  edition.)     Price,  $4.80. 

A  great  store  of  information  about  commodities  of  commerce  and  the 
commercial  geography  of  all  countries.     Especially  valuable  for  reference. 
Coman:   The  Industrial  History  of  the  United  States.    New  York:   The  Macmillan 
Co.,  1905.     Price,  $1.60. 

Outlines  the  growth  and  expansion  of  the  commerce  and  industries  of  the 
■  United  States. 
**  Davis:  Physical  Geography.    Boston;   Ginn  and  Co.,  i8q8.     Price,  $1.25. 

Treats  especially  the  life  history  of  land  forms.    Excellent  for  discussion  of 
coastal  plains,  stages  of  river  development,  and  climatic  control  of  land  forms. 
Day:    A  History  of  Commerce.    New  York:    Longmans,  Green  and  Co.,  1907. 
Price,  $1.75. 

Mainly  historical,  but  traces  many  relations  between  earth  features  and 
the  development  of  commerce  since  the  earliest  times. 
Dondlinger:    The  Book  of  Wheat.    New  York:   Orange  Judd  Co.,  1912.     Price, 
$2.00. 

An  exhaustive  discussion  of  the  factors  affecting  the  distribution  of  the 
world's  wheat  regions,  together  with  all  other  aspects  of  wheat  as  a  crop  and 
a  commodity  of  commerce. 
Dutton:  Earthquakes.    New  York:  G.  P.  Putnam's  Sons,  1904.     Price,  $2.00. 

Detailed,  scientific  treatise,  covering  the  nature  of  earthquakes,  their 
causes,  the  phenomena  associated  with  them,  and  the  leading  features  of  the 
earthquake  regions  of  the  world. 
Geikie,  James:  Earth  Sculpture.    New  York:  G.  P.  Putnam's  Sons,  1898.     Price, 
$2.00, 

Devoted  entirely  to  the  origin  and  development  of  land  forms.  Especially 
good  for  the  effects  of  geological  structure  on  topographic  forms,  and  for 
glacial  action. 


REFERENCE  BOOKS 

*  Geikie,  Sir  A.:   Elementary  Lessons  in  Physical  Geography.    New  York:    The 

Macmillan  Co.,  1900.     Price,  $r.io. 

A  simple  and  entertaining  description  of  the  more  important  aspects  oi 
physical  geography. 
Geikie,  Sir  A.:    Scenery  of  Scotland.     New  York:    The  Macmillan  Co.,  1901. 
Price,  $3.25. 

Most  interesting  reading,  full  of  information  about  processes  of  weather- 
ing and  erosion,  and  particularly  about  features  due  to  glaciation.     Has  a 
good  chapter  on  the  influence  of  physiography  on  the  people  of  Scotland. 
"^  Gifford:   Practical  Forestry.    New  York:   D.  Appleton  and  Co.,  1902.     Price, 
$1.20. 

Simple,  effective  statements  of  the  relations  of  forests  to  soils  and  stream 
flow,  the  factors  affecting  the  distribution  of  forests,  and  the  industrial  im- 
portance of  forests. 
**Herbertson:    Man  and  his  Work.     New  York:    The  Macmillan  Co.,  1902. 
Price,  60  cent's. 

A  very  suggestive  discussion  of  man's  relations  to  his  surroundings. 
Herbertson:    Descriptive  Geographies:    one  volume  each  for  North  America; 
Central  and  South  America;  Europe;  Africa;  Asia;  Australia  and  Occanica. 
New  York:  The  Macmillan  Co.,  1902-1903.     Price,  70  to  90  cents  per  v-olume. 

Collections  of  the  best  descriptions  of  typical  sections  of  the  different 
continents.    Interesting  and  instructive  supplementary  reading. 
Hogarth:  The  Nearer  East.   New  York:  D.  Appleton  and  Co.,  1902.     Price,$2.oo. 

A  regional  study  of  Balkan  Europe,  Western  Asia,  and  Egj^pt;  considers 
fully  the  physiography  and  climate  of  these  regions,  and  their  relations  to  the 
life  of  the  people. 

*  Holdich:  India.    New  York:  D.  Appleton  and  Co.,  1905.     Price,  $2.50. 

Covers  thoroughly  every  phase  of  the  geography  of  British  India.    Espe- 
cially good  for  the  study  of  life  conditions  in  a  monsoon  region. 
*Hunt:    The  Cereals  in  America.    New  York:    Orange  Judd  Co.,  1908.     Price, 

E.xcellent  for  details  concerning  soil  and  climatic  requirements  of  cereal 
crops. 
Johnson,  E.  R.:  Ocean  and  Inland  Water  Transportation.    New  York:   D.  Apple- 
ton  and  Co.,  1906.     Price,  $1.50. 

Discusses  fully  the  commercial  importance  of  inland  waterways  and  the 
chief  problems  in  their  use  for  navigation. 

*  Johnson,  W.  E.:    Mathematical  Geography.    New  York:    American  Book  Co., 

1907.  Price,  $1.00. 

A  standard  reference  for  all  matters  concerning  the  form,  motions,  and 
dimensions  of  the  earth,  and  for  tides  and  map  making. 
Johnstone:    Conditions  of  Life  in  the  Sea.     New  York:    G.  P.  Putnam's  Sons, 

1908.  Price,  $3.00. 

Describes  the  plants  and  animals  of  the  sea,  their  distribution,  and  their 
uses  by  man.  Good  also  for  methods  of  exploration  of  the  sea  and  the  main 
features  of  the  North  Atlantic  Ocean. 

*  Keltie  (Editor) :    The  Statesman's  Yearbook.    New  York:   The  Macmillan  Co., 

1863-1911.     Price,  $3.00. 

An  annual  publication  giving  current  statistics  for  all  countries.     Gives 
also  brief  statements  about  government,  education,  currency,  defence,  etc., 
for  most  countries. 
*King:    Farmers  of  Forty  Centuries.     Madison,  Wis.:    Mrs.  F.  H.  King,  1911. 
Price,  $2.50. 

Describes  agricultural  systems  of  China  and  Japan,  and  tells  much  about 
the  effects  of  geography  on  the  life  of  the  people. 


REFERENCE   BOOKS 

**King:   The  Soil.    New  York:  The  Macmillan  Co.,  igoy.     Price,  $1.50. 

An  exhaustive,  but  simple,  description  of  soil  types,  their  formation,  and 
characteristics.    Especially  good  for  discussion  of  soil  moisture. 
**King:  Irrigation  and  Drainage.    New  York:  The  Macmillan  Co.,  1909.     Price, 
$1.50. 

Treats  in  detail  the  relation  of  water  to  plant  growth,  the  soil  and  climatic 
conditions  -vhich  make  irrigation  necessary,  the  effectiveness  of  conserving 
water  by  tillage,  and  the  general  problems  of  irrigation  farming.  Wet  lands 
and  their  drainage  are  considered  more  briefly. 
Kirchoff:  Man  and  Earth.  New  York:  E.  P.  Dutton  and  Co.,  (n.d.p.).  Price, 
75  cents. 

A  small  book  with  many  good  examples  of  man's  relations  to  his  surround- 
ings, especially  in  Great  Britain,  the  United  States,  Germany,  and  China. 
Little:   The  Far  East.    New  York:   D.  Appleton  and  Co.,  1905.     Price,  $2.00. 

A  regional  study  of  China  and  Japan  along  the  same  lines  as  Hogarth's 
"The  Nearer  East"  (q.v.). 
Lyde:    Man  and  his  Markets.     New  York:    The  Macmillan  Co.,  1901.     Price, 
50  cents. 

Good  material  on  many  of  the  larger  aspects  of  commercial  geography, 
presented  in  a  new  way. 
*Mackikder:   Britain  and  the  British  Seas.    New  York:   D.  Appleton  and  Co., 
1902.     Price,  $2.00. 

A  comprehensive  study  of  every  phase  of  the  geography  of  the  British 
Isles.     Especially  valuable  for  the  ten  chapters  tracing  the  effects  of  physical 
conditions  on  the  development  of  the  four  countries. 
Me.\d:  Story  of  Gold.    New  York:  D.  Appleton  and  Co.,  1906.       Price,  75  cents. 
Describes  the  conditions  of  occurrence  of  gold,  the  methods  of  mining,  the 
chief  gold  regions  of  the  world,  and  the  importance  of  gold  in  industry  and 
coinage. 
Milham:  Meteorology.    New  York:  The  Macmillan  Co.,  1912.     Price,  $4.50. 

Embodies  the  latest  results  of  the  investigation  of  atmospheric  phenomena. 
Especially  good  on  atmospheric  moisture  and  irregular  winds. 
**  Mill  (Editor) :  The  International  Geography.    New  York:  D.  Appleton  and  Co., 

1905.  Price,  $3.50.  _ 

A  handbook  giving  the  main  geographical  aspects  of  all  countries,  by 
seventy  authors. 
Mux:    The  Realm  of  Nature.    New  York:    Chas.  Scribner's  Sons,  1892.     Price, 
$1.50. 

An  elementary  and   stimulating   treatment   of  physiography  from   the 
English  viewpoint.     Traces  the  interdependence  of  the  different  aspects  of 
nature. 
*  Moore,  W.  L.:    De-,criptivc  Meteorology.     New  York:  D.  Appleton  and  Co., 
1910.     Price,  $3.00. 

A  general  text,  less  advanced  than  Milham  (q.v.);  especially  good  for 
methods  of  weather  forecasting.     An  appendix  of  45  valuable  charts. 
*Moulton:    An  Introduction  to  Astronomy.     New  York:    The  Macmillan  Co., 

1906.  Price,  $1.60. 

A  clear,  comprehensive  exposition  of  modern  astronomy.    Especially  good 
for  discussion  of  the  evolution  of  the  solar  system,  and  the  planetary  relations 
of  the  earth. 
Newell:  Irrigation.    New  York:  T.  Y.  Crowell  and  Co.,  1906.     Price,  $2.00. 

Describes  in  detail  the  conditions  of  arid  United  States,  the  supplies  of 
water,  the  methods  of  storing  and  distributing  water,  irrigation  law,  the 
irrigated  regions  of  the  West,  and  the  relation  of  irrigation  to  crops  in  the  other 
parts  of  the  country. 


REFERENCE  BOOKS 

Partsch:  Central  Europe.    New  York:  D.  Appleton  and  Co.,  1903.     Price.  $2.00. 
Deals  mainly  with  Germany  and  Austria-Hungary  in  a  manner  similai 
to  Hogarth's  "The  Nearer  East"  (q.v.). 
Russell:  North  America.    New  York:  D.  Appleton  and  Co.,  1904.     Price,  $2.00. 
Treats  in  detail  the  coasts,  topography,  geology,  and  climate  of  the  United 
States,  and  considers  less  fully  the  other  parts  of  the  continent.     Discusses 
also  distribution  of  plant  and  animal  life. 
Russell:  Glaciers  of  North  America.    Boston:  Ginn  and  Co.,  1897.     Price,  $1.75. 
Same  type  of  book  as  Russell's  "Rivers  of  North  America"  (q.v.). 

*  Russell:   Rivers  of  North  America.    New  York:    G.  P.  Putnam's  Sons,  1898. 

Price,  $2.00. 

An  extensive  treatment  of  the  characteristics  and  work  of  streams.    Good 
descriptions  of  the  main  river  systems  of  the  continent. 
Russell:    Volcanoes  of  North  America.    New  York:    The  Macmillan  Co.,  1897. 
Price,  $4.00. 

Same  type  of  book  as  Russell's  "Rivers  of  North  America"  (q.v.). 
RiES:  Economic  Geology.    New  York:  The  Macmillan  Co.,  1910.     Price,  $3.50. 

Explains   the   formation   and   distribution   of   mineral  deposits.     Much 
information  about  important  regions  of  mineral  production. 
*"' Salisbury:   Physiography:   Briefer  Course.    New  York:   Henry  Holt  and  Co., 
1908.     Price,  $1.50. 

A  general  text  which  emphasizes  physiographic  processes  and  their  effects 
on  land  forms. 
**SEitPLE:   Influences  of  Geographic  Environment.    New  York:   Henry  Holt  and 
Co.,  1911.     Price,  $4.00. 

Deals  mainly  with  human  responses  to  geographic  conditions  in  typical 
environments.     Large  amount  of  excellent  material  for  supplementary  reading. 
*Semple:    American  History  in  its  Geographic  Conditions.     Boston:    Houghton^ 
MifBin  and  Co.,  1903.     Price,  $3.00. 

Traces  the  influence  of  geography  on  United  States  history.     Enriches  the 

study  of  either  subject. 

Shaler:  Aspects  of  the  Earth.    New  York:  Chas.  Scribner's  Sons,  1889.    Price,  $2.50, 

A  popular  account  of  some  of  the  larger  features  of  earth  science.     Very 

suggestive  on  "Caverns  and  Cavern  Life"  and  on  "The  Origin  and  Nature 

of  Soils." 

*  Shaler:  Matt  and  the  Earth.    New  York:  Fox,  DuflSeld  and  Co.,  1905.     Price, 

$1.50. 

States  in  an  interesting  and  convincing  way  man's  dependence  on  the 
resources  of  the  earth,  and  the  need  for  conserving  them. 
Shaler:  Nature  and  Man  in  America.    New  York:   Chas.  Scribner's  Sons,  1893. 
Price,  $1.50. 

Discusses  the  influences  of  environment  on  man's  progress  in  civilization, 
and  especially  the  effects  of  the  physical  features  of  North  America  on  the  set- 
tlement and  development  of  the  continent. 
Shaler:  The  Story  of  Our  Co>itinent.    Boston:  Ginn  and  Co.,  1897.     Price,  75  cents. 
A  short,  simple  account  of  the  geologic  development  of  North  America, 
the  present  condition  of  the  continent,  and  of  some  of  the  larger  effects  of 
geography  on  the  people. 
Shaler:  Sea  and  Land.    New  York:   Chas.  Scribner's  Sons,  1894.     Price,  $2.50. 
Features  of  coasts  and  oceans,  with  their  influences  on  man.     Excellent 
for  material  on  harbors. 
Smith:    The  Story  of  Iron  a)td  Steel.     New  York:    D.  Appleton  and  Co.,  1908. 
Price,  75  cents. 

A  non-technical  description  of  the  industry  and  its  development,  par- 
ticularly in  the  United  States. 


REFERENCE  BOOKS 

*  Stanford  (Publisher) :   Compendium  of  Geography  and  Travel.    Twelve  volumes 
London:  Edward  Stanford,  1895-1908.     Price,  $5.50  per  volume. 

Volumes  for  each  of  the  continents,  describing  their  physiography,  climate, 
resources,  and  something  of  the  development  of  each  of  their  countries. 
Surface:    The  Story  of  Sugar.    New  York:    D.  Appleton  and  Co.,  1910.     Price, 
$1.00. 

Discusses  the  natural  conditions  required  for  sugar  cane  and  sugar  beets, 
the  sugar  regions  of  the  world,  the  processes  of  manufacturing  sugar,  and  its 
commercial  importance. 
Taylor:  Australia:  Physiographic  and  Economic.    Oxford,  Eng.:  Clarendon  Press, 
1911.     Price,  90  cents. 

An  excellent  analysis  of  the  natural  regions  of  Australia  and  their  relations 
to  the  economic  development  of  the  country.     Many  good  maps  and  diagrams. 
Tower:    The   Story   of  Oil.    New   York:  D.  Appleton   and   Co.,    1909.     Price, 
$1.00. 

An  account  of  the  development  of  the  petroleum  industry,  mainly  in  the 
United   States.     Discusses   also   commercial   and   industrial   importance   of 
petroleum  products. 
**VanHise:  Conservation  of  Natural  Resources  in  the  United  States.    New  York: 
The  Macmillan  Co.,  1910.     Price,  $2.00. 

Considers  our  resources  in  minerals,  forests,  waters,  and  lands;   the  ways 
in  which  their  use  now  involves  needless  waste;    and  the  remedies  which 
should  be  adopted  to  check  these  wastes.     Outlines  the  recent  Conservation 
Movement. 
**Ward:  Climate.    New  York:  G.  P.  Putnam's  Sons,  1908.     Price,  $2.00. 

A  full  description  of  all  the  important  types  of  climate,  and  of  their  influence 
on  various  human  activities. 
Warren:  Elements  of  Agricidtiire.    New  York:  The  Macmillan  Co.,  1910.     Price, 
$1.10. 

Discusses  the  conditions  of  plant  growth,  the  mineral  plant  foods,  the 
raising  of  the  chief  farm  crops  and  of  live  stock,  and  the  problems  of  farm 
management. 
*Widtsoe:    Dry    Farming.    New    York:    The    Macmillan    Co.,    191 1.     Price, 
$1.50. 

E.xplains  the  principles  of  conserving  soil  moisture,  the  water  requirements 
of  different  crops,  the  conditions  in  regions  of  scanty  rainfall,  and  states  what 
can  be  done  to  reclaim  these  regions  for  agriculture. 
Willis:  Agriculture  in  the  Tropics.     Cambridge,  Eng.:     Cambridge  University 
Press,  1909.     Price,  $2.50. 

States  concisely  the  relations  of  soil,  climate,  and  labor  to  farming  in 
tropical  lands,  with  accounts  of  the  chief  tropical  crops.  Examples  drawn 
mainly  from  Ceylon  and  India. 


GOVERNM^ENT  ,Pl!BUCATI0N3 

Much  supplementary  material  may  be  fQun,d  ii>  governrnent  oublications, 
some  of  which  are  noted  below,  ''vilh  the  addresses  .'rem  vv'hich  th^^}-  may  be  ob- 
tained. Lists  of  government  pubM'ado'l?  on  difterdit  topics,  as  geography,  may 
be  obtained  by  addressing:  The  Superintendent  of  Public  Documents,  Washington, 
D.  C. 
Bureau  of  the  Census:    Reports  and  Bi'U-tins  of  'he  Census      These  furnish 

statistical  and  other  data  conrern-ng' popuiitiori,' irdvstrifes,   etc.,   in   the 

United  States.     Address:   The  Director,  Bureau  of  the  Census,  Washington, 

D.  C. 


REFERENCE   BOOKS 

Department  of  Agriculture:  (i)  Yearbook  of  the  Department  of  Agriculture. 
An  annual  publication  containing  detailed  statistics  of  agriculture  for  the 
United  States  and  general  statistics  for  foreign  countries.  Also  has  special 
articles  bearing  on  farm  industries.  Obtainable  through  local  representatives 
in  Congress.  (2)  List  of  Publications.  A  monthly  circular  giving  titles  of 
current  publications  of  the  Department,  including  Bulletins  and  Circulars  of 
the  Forestry  Service,  and  publications  of  the  Weather  Bureau.  Address: 
The  Editor  and  Chief,  Division  of  Publications,  Dept.  of  Agriculture,  Wash- 
ington, D.  C. 

U.  S.  Geological  Survey:  (i)  Topographic  maps  of  many  parts  of  the  country; 
(2)  Mineral  Resources  of  the  United  States,  an  annual  publication;  (3)  Annual 
Reports;  (4)  Professional  Papers;  (5)  Bulletins;  and  (6)  Water  Supply  and 
Irrigation  Papers.  Many  of  the  above  contain  much  supplementary  material 
for  work  in  geography.  The  Press  Bulletins  of  the  Survey  are  leaflets  issued 
at  frequent  intervals,  which  contain  current  items  of  interest,  especially  in 
regard  to  economic  aspects  of  the  work  of  the  Bureau.  Address :  The  Director, 
U.  S.  Geological  Survey,  Washington,  D.  C. 

Department  of  Commerce  and  Labor:  (i)  Monthly  Summary  of  Commerce  and 
Finance;  (2)  Commerce  and  Navigation  of  the  United  States;  and  (3)  Com- 
mercial Relations  of  the  United  States.  These  contain  elaborate  statistical 
data  concerning  the  foreign  commerce  of  the  country.  The  last  named,  an 
annual  volume,  discusses  our  trade  with  each  foreign  country.  The  volume 
on  Commerce  and  Navigation  (annual)  gives  statistics  by  countries,  com- 
modities, and  ports  of  entry  or  shipment.  Address:  The  Secretary,  Depart- 
ment of  Commerce  and  Labor,  Washington,  D.  C. 


MAGAZINES 

The  geographical  magazines  noted  below  are  important  helps  to  students 
and  teachers  of  geography: 
Bulletin  of  the  American  Geographical  Society.    New  York:    Broadway  and  156th 

Street.     $5  per  year. 
Geographicaljournal.    London:  Royal  Geographical  Society.     27  s.  per  year. 
Journal  of  Geography.     Madison,  Wis. :  University  of  Wisconsin.    $1 .  00  per  year. 
National  Geographic  Magazine.    Washington,  D.  C:    i6th  and  M  Streets,  N.  W. 

%2 .  50  per  year. 
Scottish  Geographic  Magazine.    Edinburgh:  Royal  Scottish  Geographical  Society. 

18  s.  per  year. 


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